Getting Started with Netlify Functions for Angular

A guide to the first steps of adding serverless functions to your Angular application using Netlify Functions.

Being able to add serverless functions to your Angular application opens up a world of opportunities for getting data to your users. Netlify Functions makes it easier to utilize serverless functions by managing the infrastructure. They do this by creating a wrapper around AWS Lambda functions so that we can have the power without the pain.

🧠 We also have Background Functions in Beta if you need extended execution times.

To start us off, I wanted to show you the very fist steps:

setting up a Netlify Function in an Angular app
creating a bare-bones function
testing it locally
serving it up on Netlify &
testing it in production

This will be enough information to let us hit the ground running towards a dynamic data dynasty ✧_｡٩(ˊᗜˋ_)و✧/*｡!

⏭ Just want to fast-forward to using this function? Here is a template repo, or go even faster by using this button to deploy the project to Netlify:

#angular #netlify #web-development #javascript

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Getting Started with Netlify Functions for Angular

Shubham Ankit

1657081614

How to Automate Excel with Python | Python Excel Tutorial (OpenPyXL)

How to Automate Excel with Python

In this article, We will show how we can use python to automate Excel . A useful Python library is Openpyxl which we will learn to do Excel Automation

What is OPENPYXL

Openpyxl is a Python library that is used to read from an Excel file or write to an Excel file. Data scientists use Openpyxl for data analysis, data copying, data mining, drawing charts, styling sheets, adding formulas, and more.

Workbook: A spreadsheet is represented as a workbook in openpyxl. A workbook consists of one or more sheets.

Sheet: A sheet is a single page composed of cells for organizing data.

Cell: The intersection of a row and a column is called a cell. Usually represented by A1, B5, etc.

Row: A row is a horizontal line represented by a number (1,2, etc.).

Column: A column is a vertical line represented by a capital letter (A, B, etc.).

Openpyxl can be installed using the pip command and it is recommended to install it in a virtual environment.

pip install openpyxl

CREATE A NEW WORKBOOK

We start by creating a new spreadsheet, which is called a workbook in Openpyxl. We import the workbook module from Openpyxl and use the function Workbook() which creates a new workbook.

from openpyxl
import Workbook
#creates a new workbook
wb = Workbook()
#Gets the first active worksheet
ws = wb.active
#creating new worksheets by using the create_sheet method

ws1 = wb.create_sheet("sheet1", 0) #inserts at first position
ws2 = wb.create_sheet("sheet2") #inserts at last position
ws3 = wb.create_sheet("sheet3", -1) #inserts at penultimate position

#Renaming the sheet
ws.title = "Example"

#save the workbook
wb.save(filename = "example.xlsx")

READING DATA FROM WORKBOOK

We load the file using the function load_Workbook() which takes the filename as an argument. The file must be saved in the same working directory.

#loading a workbook
wb = openpyxl.load_workbook("example.xlsx")

GETTING SHEETS FROM THE LOADED WORKBOOK

#getting sheet names
wb.sheetnames
result = ['sheet1', 'Sheet', 'sheet3', 'sheet2']

#getting a particular sheet
sheet1 = wb["sheet2"]

#getting sheet title
sheet1.title
result = 'sheet2'

#Getting the active sheet
sheetactive = wb.active
result = 'sheet1'

ACCESSING CELLS AND CELL VALUES

#get a cell from the sheet
sheet1["A1"] <
  Cell 'Sheet1'.A1 >

  #get the cell value
ws["A1"].value 'Segment'

#accessing cell using row and column and assigning a value
d = ws.cell(row = 4, column = 2, value = 10)
d.value
10

ITERATING THROUGH ROWS AND COLUMNS

#looping through each row and column
for x in range(1, 5):
  for y in range(1, 5):
  print(x, y, ws.cell(row = x, column = y)
    .value)

#getting the highest row number
ws.max_row
701

#getting the highest column number
ws.max_column
19

There are two functions for iterating through rows and columns.

Iter_rows() => returns the rows
Iter_cols() => returns the columns {
  min_row = 4, max_row = 5, min_col = 2, max_col = 5
} => This can be used to set the boundaries
for any iteration.

Example:

#iterating rows
for row in ws.iter_rows(min_row = 2, max_col = 3, max_row = 3):
  for cell in row:
  print(cell) <
  Cell 'Sheet1'.A2 >
  <
  Cell 'Sheet1'.B2 >
  <
  Cell 'Sheet1'.C2 >
  <
  Cell 'Sheet1'.A3 >
  <
  Cell 'Sheet1'.B3 >
  <
  Cell 'Sheet1'.C3 >

  #iterating columns
for col in ws.iter_cols(min_row = 2, max_col = 3, max_row = 3):
  for cell in col:
  print(cell) <
  Cell 'Sheet1'.A2 >
  <
  Cell 'Sheet1'.A3 >
  <
  Cell 'Sheet1'.B2 >
  <
  Cell 'Sheet1'.B3 >
  <
  Cell 'Sheet1'.C2 >
  <
  Cell 'Sheet1'.C3 >

To get all the rows of the worksheet we use the method worksheet.rows and to get all the columns of the worksheet we use the method worksheet.columns. Similarly, to iterate only through the values we use the method worksheet.values.

Example:

for row in ws.values:
  for value in row:
  print(value)

WRITING DATA TO AN EXCEL FILE

Writing to a workbook can be done in many ways such as adding a formula, adding charts, images, updating cell values, inserting rows and columns, etc… We will discuss each of these with an example.

CREATING AND SAVING A NEW WORKBOOK

#creates a new workbook
wb = openpyxl.Workbook()

#saving the workbook
wb.save("new.xlsx")

ADDING AND REMOVING SHEETS

#creating a new sheet
ws1 = wb.create_sheet(title = "sheet 2")

#creating a new sheet at index 0
ws2 = wb.create_sheet(index = 0, title = "sheet 0")

#checking the sheet names
wb.sheetnames['sheet 0', 'Sheet', 'sheet 2']

#deleting a sheet
del wb['sheet 0']

#checking sheetnames
wb.sheetnames['Sheet', 'sheet 2']

ADDING CELL VALUES

#checking the sheet value
ws['B2'].value
null

#adding value to cell
ws['B2'] = 367

#checking value
ws['B2'].value
367

ADDING FORMULAS

We often require formulas to be included in our Excel datasheet. We can easily add formulas using the Openpyxl module just like you add values to a cell.

For example:

import openpyxl
from openpyxl
import Workbook

wb = openpyxl.load_workbook("new1.xlsx")
ws = wb['Sheet']

ws['A9'] = '=SUM(A2:A8)'

wb.save("new2.xlsx")

The above program will add the formula (=SUM(A2:A8)) in cell A9. The result will be as below.

MERGE/UNMERGE CELLS

Two or more cells can be merged to a rectangular area using the method merge_cells(), and similarly, they can be unmerged using the method unmerge_cells().

For example:
Merge cells

#merge cells B2 to C9
ws.merge_cells('B2:C9')
ws['B2'] = "Merged cells"

Adding the above code to the previous example will merge cells as below.

UNMERGE CELLS

#unmerge cells B2 to C9
ws.unmerge_cells('B2:C9')

The above code will unmerge cells from B2 to C9.

INSERTING AN IMAGE

To insert an image we import the image function from the module openpyxl.drawing.image. We then load our image and add it to the cell as shown in the below example.

Example:

import openpyxl
from openpyxl
import Workbook
from openpyxl.drawing.image
import Image

wb = openpyxl.load_workbook("new1.xlsx")
ws = wb['Sheet']
#loading the image(should be in same folder)
img = Image('logo.png')
ws['A1'] = "Adding image"
#adjusting size
img.height = 130
img.width = 200
#adding img to cell A3

ws.add_image(img, 'A3')

wb.save("new2.xlsx")

Result:

CREATING CHARTS

Charts are essential to show a visualization of data. We can create charts from Excel data using the Openpyxl module chart. Different forms of charts such as line charts, bar charts, 3D line charts, etc., can be created. We need to create a reference that contains the data to be used for the chart, which is nothing but a selection of cells (rows and columns). I am using sample data to create a 3D bar chart in the below example:

Example

import openpyxl
from openpyxl
import Workbook
from openpyxl.chart
import BarChart3D, Reference, series

wb = openpyxl.load_workbook("example.xlsx")
ws = wb.active

values = Reference(ws, min_col = 3, min_row = 2, max_col = 3, max_row = 40)
chart = BarChart3D()
chart.add_data(values)
ws.add_chart(chart, "E3")
wb.save("MyChart.xlsx")

Result

How to Automate Excel with Python with Video Tutorial

Welcome to another video! In this video, We will cover how we can use python to automate Excel. I'll be going over everything from creating workbooks to accessing individual cells and stylizing cells. There is a ton of things that you can do with Excel but I'll just be covering the core/base things in OpenPyXl.

📄 Resources 📄
OpenPyXL Docs: https://openpyxl.readthedocs.io/en/stable/
Code Written in This Tutorial: https://github.com/techwithtim/ExcelPythonTutorial
Subscribe: https://www.youtube.com/c/TechWithTim/featured

#python

Arvilla Medhurst

1661592007

A Collection Of Swift Tips & Tricks That I've Shared on Twitter

⚠️ This list is no longer being updated. For my latest Swift tips, checkout the "Tips" section on Swift by Sundell.

Swift tips & tricks ⚡️

One of the things I really love about Swift is how I keep finding interesting ways to use it in various situations, and when I do - I usually share them on Twitter. Here's a collection of all the tips & tricks that I've shared so far. Each entry has a link to the original tweet, if you want to respond with some feedback or question, which is always super welcome! 🚀

Also make sure to check out all of my other Swift content:

#102 Making async tests faster and more stable

🚀 Here are some quick tips to make async tests faster & more stable:

😴 Avoid sleep() - use expectations instead
⏱ Use generous timeouts to avoid flakiness on CI
🧐 Put all assertions at the end of each test, not inside closures

// BEFORE:

class MentionDetectorTests: XCTestCase {
    func testDetectingMention() {
        let detector = MentionDetector()
        let string = "This test was written by @johnsundell."

        detector.detectMentions(in: string) { mentions in
            XCTAssertEqual(mentions, ["johnsundell"])
        }
        
        sleep(2)
    }
}

// AFTER:

class MentionDetectorTests: XCTestCase {
    func testDetectingMention() {
        let detector = MentionDetector()
        let string = "This test was written by @johnsundell."

        var mentions: [String]?
        let expectation = self.expectation(description: #function)

        detector.detectMentions(in: string) {
            mentions = $0
            expectation.fulfill()
        }

        waitForExpectations(timeout: 10)
        XCTAssertEqual(mentions, ["johnsundell"])
    }
}

For more on async testing, check out "Unit testing asynchronous Swift code".

#101 Adding support for Apple Pencil double-taps

✍️ Adding support for the new Apple Pencil double-tap feature is super easy! All you have to do is to create a UIPencilInteraction, add it to a view, and implement one delegate method. Hopefully all pencil-compatible apps will soon adopt this.

let interaction = UIPencilInteraction()
interaction.delegate = self
view.addInteraction(interaction)

extension ViewController: UIPencilInteractionDelegate {
    func pencilInteractionDidTap(_ interaction: UIPencilInteraction) {
        // Handle pencil double-tap
    }
}

For more on using this and other iPad Pro features, check out "Building iPad Pro features in Swift".

#100 Combining values with functions

😎 Here's a cool function that combines a value with a function to return a closure that captures that value, so that it can be called without any arguments. Super useful when working with closure-based APIs and we want to use some of our properties without having to capture self.

func combine<A, B>(_ value: A, with closure: @escaping (A) -> B) -> () -> B {
    return { closure(value) }
}

// BEFORE:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = { [weak self] in
            guard let self = self else {
                return
            }
            
            self.productManager.startCheckout(for: self.product)
        }
    }
}

// AFTER:

class ProductViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        buyButton.handler = combine(product, with: productManager.startCheckout)
    }
}

#99 Dependency injection using functions

💉 When I'm only using a single function from a dependency, I love to inject that function as a closure, instead of having to create a protocol and inject the whole object. Makes dependency injection & testing super simple.

final class ArticleLoader {
    typealias Networking = (Endpoint) -> Future<Data>
    
    private let networking: Networking
    
    init(networking: @escaping Networking = URLSession.shared.load) {
        self.networking = networking
    }
    
    func loadLatest() -> Future<[Article]> {
        return networking(.latestArticles).decode()
    }
}

For more on this technique, check out "Simple Swift dependency injection with functions".

#98 Using a custom exception handler

💥 It's cool that you can easily assign a closure as a custom NSException handler. This is super useful when building things in Playgrounds - since you can't use breakpoints - so instead of just signal SIGABRT, you'll get the full exception description if something goes wrong.

NSSetUncaughtExceptionHandler { exception in
    print(exception)
}

#97 Using type aliases to give semantic meaning to primitives

❤️ I love that in Swift, we can use the type system to make our code so much more self-documenting - one way of doing so is to use type aliases to give the primitive types that we use a more semantic meaning.

extension List.Item {
    // Using type aliases, we can give semantic meaning to the
    // primitive types that we use, without having to introduce
    // wrapper types.
    typealias Index = Int
}

extension List {
    enum Mutation {
        // Our enum cases now become a lot more self-documenting,
        // without having to add additional parameter labels to
        // explain them.
        case add(Item, Item.Index)
        case update(Item, Item.Index)
        case remove(Item.Index)
    }
}

For more on self-documenting code, check out "Writing self-documenting Swift code".

#96 Specializing protocols using constraints

🤯 A little late night prototyping session reveals that protocol constraints can not only be applied to extensions - they can also be added to protocol definitions!

This is awesome, since it lets us easily define specialized protocols based on more generic ones.

protocol Component {
    associatedtype Container
    func add(to container: Container)
}

// Protocols that inherit from other protocols can include
// constraints to further specialize them.
protocol ViewComponent: Component where Container == UIView {
    associatedtype View: UIView
    var view: View { get }
}

extension ViewComponent {
    func add(to container: UIView) {
        container.addSubview(view)
    }
}

For more on specializing protocols, check out "Specializing protocols in Swift".

#95 Unwrapping an optional or throwing an error

📦 Here's a super handy extension on Swift's Optional type, which gives us a really nice API for easily unwrapping an optional, or throwing an error in case the value turned out to be nil:

extension Optional {
    func orThrow(_ errorExpression: @autoclosure () -> Error) throws -> Wrapped {
        switch self {
        case .some(let value):
            return value
        case .none:
            throw errorExpression()
        }
    }
}

let file = try loadFile(at: path).orThrow(MissingFileError())

For more ways that optionals can be extended, check out "Extending optionals in Swift".

#94 Testing code that uses static APIs

👩‍🔬 Testing code that uses static APIs can be really tricky, but there's a way that it can often be done - using Swift's first class function capabilities!

Instead of accessing that static API directly, we can inject the function we want to use, which enables us to mock it!

// BEFORE

class FriendsLoader {
    func loadFriends(then handler: @escaping (Result<[Friend]>) -> Void) {
        Networking.loadData(from: .friends) { result in
            ...
        }
    }
}

// AFTER

class FriendsLoader {
    typealias Handler<T> = (Result<T>) -> Void
    typealias DataLoadingFunction = (Endpoint, @escaping Handler<Data>) -> Void

    func loadFriends(using dataLoading: DataLoadingFunction = Networking.loadData,
                     then handler: @escaping Handler<[Friend]>) {
        dataLoading(.friends) { result in
            ...
        }
    }
}

// MOCKING IN TESTS

let dataLoading: FriendsLoader.DataLoadingFunction = { _, handler in
    handler(.success(mockData))
}

friendsLoader.loadFriends(using: dataLoading) { result in
    ...
}

#93 Matching multiple enum cases with associated values

🐾 Swift's pattern matching capabilities are so powerful! Two enum cases with associated values can even be matched and handled by the same switch case - which is super useful when handling state changes with similar data.

enum DownloadState {
    case inProgress(progress: Double)
    case paused(progress: Double)
    case cancelled
    case finished(Data)
}

func downloadStateDidChange(to state: DownloadState) {
    switch state {
    case .inProgress(let progress), .paused(let progress):
        updateProgressView(with: progress)
    case .cancelled:
        showCancelledMessage()
    case .finished(let data):
        process(data)
    }
}

#92 Multiline string literals

🅰 One really nice benefit of Swift multiline string literals - even for single lines of text - is that they don't require quotes to be escaped. Perfect when working with things like HTML, or creating a custom description for an object.

let html = highlighter.highlight("Array<String>")

XCTAssertEqual(html, """
<span class="type">Array</span>&lt;<span class="type">String</span>&gt;
""")

#91 Reducing sequences

💎 While it's very common in functional programming, the reduce function might be a bit of a hidden gem in Swift. It provides a super useful way to transform a sequence into a single value.

extension Sequence where Element: Equatable {
    func numberOfOccurrences(of target: Element) -> Int {
        return reduce(0) { result, element in
            guard element == target else {
                return result
            }

            return result + 1
        }
    }
}

You can read more about transforming collections in "Transforming collections in Swift".

#90 Avoiding manual Codable implementations

📦 When I use Codable in Swift, I want to avoid manual implementations as much as possible, even when there's a mismatch between my code structure and the JSON I'm decoding.

One way that can often be achieved is to use private data containers combined with computed properties.

struct User: Codable {
    let name: String
    let age: Int

    var homeTown: String { return originPlace.name }

    private let originPlace: Place
}

private extension User {
    struct Place: Codable {
        let name: String
    }
}

extension User {
    struct Container: Codable {
        let user: User
    }
}

#89 Using feature flags instead of feature branches

🚢 Instead of using feature branches, I merge almost all of my code directly into master - and then I use feature flags to conditionally enable features when they're ready. That way I can avoid merge conflicts and keep shipping!

extension ListViewController {
    func addSearchIfNeeded() {
        // Rather than having to keep maintaining a separate
        // feature branch for a new feature, we can use a flag
        // to conditionally turn it on.
        guard FeatureFlags.searchEnabled else {
            return
        }

        let resultsVC = SearchResultsViewController()
        let searchVC = UISearchController(
            searchResultsController: resultsVC
        )

        searchVC.searchResultsUpdater = resultsVC
        navigationItem.searchController = searchVC
    }
}

You can read more about feature flags in "Feature flags in Swift".

#88 Lightweight data hierarchies using tuples

💾 Here I'm using tuples to create a lightweight hierarchy for my data, giving me a nice structure without having to introduce any additional types.

struct CodeSegment {
    var tokens: (
        previous: String?,
        current: String
    )

    var delimiters: (
        previous: Character?
        next: Character?
    )
}

handle(segment.tokens.current)

You can read more about tuples in "Using tuples as lightweight types in Swift"

#87 The rule of threes

3️⃣ Whenever I have 3 properties or local variables that share the same prefix, I usually try to extract them into their own method or type. That way I can avoid massive types & methods, and also increase readability, without falling into a "premature optimization" trap.

Before

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")

    let articleFolder = try contentFolder.subfolder(named: "posts")
    let articleProcessor = ContentProcessor(folder: articleFolder)
    let articles = try articleProcessor.process()

    ...
}

After

public func generate() throws {
    let contentFolder = try folder.subfolder(named: "content")
    let articles = try processArticles(in: contentFolder)
    ...
}

private func processArticles(in folder: Folder) throws -> [ContentItem] {
    let folder = try folder.subfolder(named: "posts")
    let processor = ContentProcessor(folder: folder)
    return try processor.process()
}

#86 Useful Codable extensions

👨‍🔧 Here's two extensions that I always add to the Encodable & Decodable protocols, which for me really make the Codable API nicer to use. By using type inference for decoding, a lot of boilerplate can be removed when the compiler is already able to infer the resulting type.

extension Encodable {
    func encoded() throws -> Data {
        return try JSONEncoder().encode(self)
    }
}

extension Data {
    func decoded<T: Decodable>() throws -> T {
        return try JSONDecoder().decode(T.self, from: self)
    }
}

let data = try user.encoded()

// By using a generic type in the decoded() method, the
// compiler can often infer the type we want to decode
// from the current context.
try userDidLogin(data.decoded())

// And if not, we can always supply the type, still making
// the call site read very nicely.
let otherUser = try data.decoded() as User

#85 Using shared UserDefaults suites

📦 UserDefaults is a lot more powerful than what it first might seem like. Not only can it store more complex values (like dates & dictionaries) and parse command line arguments - it also enables easy sharing of settings & lightweight data between apps in the same App Group.

let sharedDefaults = UserDefaults(suiteName: "my-app-group")!
let useDarkMode = sharedDefaults.bool(forKey: "dark-mode")

// This value is put into the shared suite.
sharedDefaults.set(true, forKey: "dark-mode")

// If you want to treat the shared settings as read-only (and add
// local overrides on top of them), you can simply add the shared
// suite to the standard UserDefaults.
let combinedDefaults = UserDefaults.standard
combinedDefaults.addSuite(named: "my-app-group")

// This value is a local override, not added to the shared suite.
combinedDefaults.set(true, forKey: "app-specific-override")

#84 Custom UIView backing layers

🎨 By overriding layerClass you can tell UIKit what CALayer class to use for a UIView's backing layer. That way you can reduce the amount of layers, and don't have to do any manual layout.

final class GradientView: UIView {
    override class var layerClass: AnyClass { return CAGradientLayer.self }

    var colors: (start: UIColor, end: UIColor)? {
        didSet { updateLayer() }
    }

    private func updateLayer() {
        let layer = self.layer as! CAGradientLayer
        layer.colors = colors.map { [$0.start.cgColor, $0.end.cgColor] }
    }
}

#83 Auto-Equatable enums with associated values

✅ That the compiler now automatically synthesizes Equatable conformances is such a huge upgrade for Swift! And the cool thing is that it works for all kinds of types - even for enums with associated values! Especially useful when using enums for verification in unit tests.

struct Article: Equatable {
    let title: String
    let text: String
}

struct User: Equatable {
    let name: String
    let age: Int
}

extension Navigator {
    enum Destination: Equatable {
        case profile(User)
        case article(Article)
    }
}

func testNavigatingToArticle() {
    let article = Article(title: "Title", text: "Text")
    controller.select(article)
    XCTAssertEqual(navigator.destinations, [.article(article)])
}

#82 Defaults for associated types

🤝 Associated types can have defaults in Swift - which is super useful for types that are not easily inferred (for example when they're not used for a specific instance method or property).

protocol Identifiable {
    associatedtype RawIdentifier: Codable = String

    var id: Identifier<Self> { get }
}

struct User: Identifiable {
    let id: Identifier<User>
    let name: String
}

struct Group: Identifiable {
    typealias RawIdentifier = Int

    let id: Identifier<Group>
    let name: String
}

#81 Creating a dedicated identifier type

🆔 If you want to avoid using plain strings as identifiers (which can increase both type safety & readability), it's really easy to create a custom Identifier type that feels just like a native Swift type, thanks to protocols!

More on this topic in "Type-safe identifiers in Swift".

struct Identifier: Hashable {
    let string: String
}

extension Identifier: ExpressibleByStringLiteral {
    init(stringLiteral value: String) {
        string = value
    }
}

extension Identifier: CustomStringConvertible {
    var description: String {
        return string
    }
}

extension Identifier: Codable {
    init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        string = try container.decode(String.self)
    }

    func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encode(string)
    }
}

struct Article: Codable {
    let id: Identifier
    let title: String
}

let article = Article(id: "my-article", title: "Hello world!")

#80 Assigning optional tuple members to variables

🙌 A really cool thing about using tuples to model the internal state of a Swift type, is that you can unwrap an optional tuple's members directly into local variables.

Very useful in order to group multiple optional values together for easy unwrapping & handling.

class ImageTransformer {
    private var queue = [(image: UIImage, transform: Transform)]()

    private func processNext() {
        // When unwrapping an optional tuple, you can assign the members
        // directly to local variables.
        guard let (image, transform) = queue.first else {
            return
        }

        let context = Context()
        context.draw(image)
        context.apply(transform)
        ...
    }
}

#79 Struct convenience initializers

❤️ I love to structure my code using extensions in Swift. One big benefit of doing so when it comes to struct initializers, is that defining a convenience initializer doesn't remove the default one the compiler generates - best of both worlds!

struct Article {
    let date: Date
    var title: String
    var text: String
    var comments: [Comment]
}

extension Article {
    init(title: String, text: String) {
        self.init(date: Date(), title: title, text: text, comments: [])
    }
}

let articleA = Article(title: "Best Cupcake Recipe", text: "...")

let articleB = Article(
    date: Date(),
    title: "Best Cupcake Recipe",
    text: "...",
    comments: [
        Comment(user: currentUser, text: "Yep, can confirm!")
    ]
)

#78 Usages of throwing functions

🏈 A big benefit of using throwing functions for synchronous Swift APIs is that the caller can decide whether they want to treat the return value as optional (try?) or required (try).

func loadFile(named name: String) throws -> File {
    guard let url = urlForFile(named: name) else {
        throw File.Error.missing
    }

    do {
        let data = try Data(contentsOf: url)
        return File(url: url, data: data)
    } catch {
        throw File.Error.invalidData(error)
    }
}

let requiredFile = try loadFile(named: "AppConfig.json")

let optionalFile = try? loadFile(named: "UserSettings.json")

#77 Nested generic types

🐝 Types that are nested in generics automatically inherit their parent's generic types - which is super useful when defining accessory types (for things like states or outcomes).

struct Task<Input, Output> {
    typealias Closure = (Input) throws -> Output

    let closure: Closure
}

extension Task {
    enum Result {
        case success(Output)
        case failure(Error)
    }
}

#76 Equatable & Hashable structures

🤖 Now that the Swift compiler automatically synthesizes Equatable & Hashable conformances for value types, it's easier than ever to setup model structures with nested types that are all Equatable/Hashable!

typealias Value = Hashable & Codable

struct User: Value {
    var name: String
    var age: Int
    var lastLoginDate: Date?
    var settings: Settings
}

extension User {
    struct Settings: Value {
        var itemsPerPage: Int
        var theme: Theme
    }
}

extension User.Settings {
    enum Theme: String, Value {
        case light
        case dark
    }
}

#75 Conditional conformances

🎉 Swift 4.1 is here! One of the key features it brings is conditional conformances, which lets you have a type only conform to a protocol under certain constraints.

protocol UnboxTransformable {
    associatedtype RawValue

    static func transform(_ value: RawValue) throws -> Self?
}

extension Array: UnboxTransformable where Element: UnboxTransformable {
    typealias RawValue = [Element.RawValue]

    static func transform(_ value: RawValue) throws -> [Element]? {
        return try value.compactMap(Element.transform)
    }
}

I also have an article with lots of more info on conditional conformances here. Paul Hudson also has a great overview of all Swift 4.1 features here.

#74 Generic type aliases

🕵️‍♀️ A cool thing about Swift type aliases is that they can be generic! Combine that with tuples and you can easily define simple generic types.

typealias Pair<T> = (T, T)

extension Game {
    func calculateScore(for players: Pair<Player>) -> Int {
        ...
    }
}

You can read more about using tuples as lightweight types here.

#73 Parsing command line arguments using UserDefaults

☑️ A really cool "hidden" feature of UserDefaults is that it contains any arguments that were passed to the app at launch!

Super useful both in Swift command line tools & scripts, but also to temporarily override a value when debugging iOS apps.

let defaults = UserDefaults.standard
let query = defaults.string(forKey: "query")
let resultCount = defaults.integer(forKey: "results")

#72 Using the & operator

👏 Swift's & operator is awesome! Not only can you use it to compose protocols, you can compose other types too! Very useful if you want to hide concrete types & implementation details.

protocol LoadableFromURL {
    func load(from url: URL)
}

class ContentViewController: UIViewController, LoadableFromURL {
    func load(from url: URL) {
        ...
    }
}

class ViewControllerFactory {
    func makeContentViewController() -> UIViewController & LoadableFromURL {
        return ContentViewController()
    }
}

#71 Capturing multiple values in mocks

🤗 When capturing values in mocks, using an array (instead of just a single value) makes it easy to verify that only a certain number of values were passed.

Perfect for protecting against "over-calling" something.

class UserManagerTests: XCTestCase {
    func testObserversCalledWhenUserFirstLogsIn() {
        let manager = UserManager()

        let observer = ObserverMock()
        manager.addObserver(observer)

        // First login, observers should be notified
        let user = User(id: 123, name: "John")
        manager.userDidLogin(user)
        XCTAssertEqual(observer.users, [user])

        // If the same user logs in again, observers shouldn't be notified
        manager.userDidLogin(user)
        XCTAssertEqual(observer.users, [user])
    }
}

private extension UserManagerTests {
    class ObserverMock: UserManagerObserver {
        private(set) var users = [User]()

        func userDidChange(to user: User) {
            users.append(user)
        }
    }
}

#70 Reducing the need for mocks

👋 When writing tests, you don't always need to create mocks - you can create stubs using real instances of things like errors, URLs & UserDefaults.

Here's how to do that for some common tasks/object types in Swift:

// Create errors using NSError (#function can be used to reference the name of the test)
let error = NSError(domain: #function, code: 1, userInfo: nil)

// Create non-optional URLs using file paths
let url = URL(fileURLWithPath: "Some/URL")

// Reference the test bundle using Bundle(for:)
let bundle = Bundle(for: type(of: self))

// Create an explicit UserDefaults object (instead of having to use a mock)
let userDefaults = UserDefaults(suiteName: #function)

// Create queues to control/await concurrent operations
let queue = DispatchQueue(label: #function)

For when you actually do need mocking, check out "Mocking in Swift".

#69 Using "then" as an external parameter label for closures

⏱ I've started using "then" as an external parameter label for completion handlers. Makes the call site read really nicely (Because I do ❤️ conversational API design) regardless of whether trailing closure syntax is used or not.

protocol DataLoader {
    // Adding type aliases to protocols can be a great way to
    // reduce verbosity for parameter types.
    typealias Handler = (Result<Data>) -> Void
    associatedtype Endpoint

    func loadData(from endpoint: Endpoint, then handler: @escaping Handler)
}

loader.loadData(from: .messages) { result in
    ...
}

loader.loadData(from: .messages, then: { result in
    ...
})

#68 Combining lazily evaluated sequences with the builder pattern

😴 Combining lazily evaluated sequences with builder pattern-like properties can lead to some pretty sweet APIs for configurable sequences in Swift.

Also useful for queries & other things you "build up" and then execute.

// Extension adding builder pattern-like properties that return
// a new sequence value with the given configuration applied
extension FileSequence {
    var recursive: FileSequence {
        var sequence = self
        sequence.isRecursive = true
        return sequence
    }

    var includingHidden: FileSequence {
        var sequence = self
        sequence.includeHidden = true
        return sequence
    }
}

// BEFORE

let files = folder.makeFileSequence(recursive: true, includeHidden: true)

// AFTER

let files = folder.files.recursive.includingHidden

Want an intro to lazy sequences? Check out "Swift sequences: The art of being lazy".

#67 Faster & more stable UI tests

My top 3 tips for faster & more stable UI tests:

📱 Reset the app's state at the beginning of every test.

🆔 Use accessibility identifiers instead of UI strings.

⏱ Use expectations instead of waiting time.

func testOpeningArticle() {
    // Launch the app with an argument that tells it to reset its state
    let app = XCUIApplication()
    app.launchArguments.append("--uitesting")
    app.launch()
    
    // Check that the app is displaying an activity indicator
    let activityIndicator = app.activityIndicator.element
    XCTAssertTrue(activityIndicator.exists)
    
    // Wait for the loading indicator to disappear = content is ready
    expectation(for: NSPredicate(format: "exists == 0"),
                evaluatedWith: activityIndicator)
                
    // Use a generous timeout in case the network is slow
    waitForExpectations(timeout: 10)
    
    // Tap the cell for the first article
    app.tables.cells["Article.0"].tap()
    
    // Assert that a label with the accessibility identifier "Article.Title" exists
    let label = app.staticTexts["Article.Title"]
    XCTAssertTrue(label.exists)
}

#66 Accessing the clipboard from a Swift script

📋 It's super easy to access the contents of the clipboard from a Swift script. A big benefit of Swift scripting is being able to use Cocoa's powerful APIs for Mac apps.

import Cocoa

let clipboard = NSPasteboard.general.string(forType: .string)

#65 Using tuples for view state

🎯 Using Swift tuples for view state can be a super nice way to group multiple properties together and render them reactively using the layout system.

By using a tuple we don't have to either introduce a new type or make our view model-aware.

class TextView: UIView {
    var state: (title: String?, text: String?) {
        // By telling UIKit that our view needs layout and binding our
        // state in layoutSubviews, we can react to state changes without
        // doing unnecessary layout work.
        didSet { setNeedsLayout() }
    }

    private let titleLabel = UILabel()
    private let textLabel = UILabel()

    override func layoutSubviews() {
        super.layoutSubviews()

        titleLabel.text = state.title
        textLabel.text = state.text

        ...
    }
}

#64 Throwing tests and LocalizedError

⚾️ Swift tests can throw, which is super useful in order to avoid complicated logic or force unwrapping. By making errors conform to LocalizedError, you can also get a nice error message in Xcode if there's a failure.

class ImageCacheTests: XCTestCase {
    func testCachingAndLoadingImage() throws {
        let bundle = Bundle(for: type(of: self))
        let cache = ImageCache(bundle: bundle)
        
        // Bonus tip: You can easily load images from your test
        // bundle using this UIImage initializer
        let image = try require(UIImage(named: "sample", in: bundle, compatibleWith: nil))
        try cache.cache(image, forKey: "key")
        
        let cachedImage = try cache.image(forKey: "key")
        XCTAssertEqual(image, cachedImage)
    }
}

enum ImageCacheError {
    case emptyKey
    case dataConversionFailed
}

// When using throwing tests, making your errors conform to
// LocalizedError will render a much nicer error message in
// Xcode (per default only the error code is shown).
extension ImageCacheError: LocalizedError {
    var errorDescription: String? {
        switch self {
        case .emptyKey:
            return "An empty key was given"
        case .dataConversionFailed:
            return "Failed to convert the given image to Data"
        }
    }
}

For more information, and the implementation of the require method used above, check out "Avoiding force unwrapping in Swift unit tests".

#63 The difference between static and class properties

✍️ Unlike static properties, class properties can be overridden by subclasses (however, they can't be stored, only computed).

class TableViewCell: UITableViewCell {
    class var preferredHeight: CGFloat { return 60 }
}

class TallTableViewCell: TableViewCell {
    override class var preferredHeight: CGFloat { return 100 }
}

#62 Creating extensions with static factory methods

👨‍🎨 Creating extensions with static factory methods can be a great alternative to subclassing in Swift, especially for things like setting up UIViews, CALayers or other kinds of styling.

It also lets you remove a lot of styling & setup from your view controllers.

extension UILabel {
    static func makeForTitle() -> UILabel {
        let label = UILabel()
        label.font = .boldSystemFont(ofSize: 24)
        label.textColor = .darkGray
        label.adjustsFontSizeToFitWidth = true
        label.minimumScaleFactor = 0.75
        return label
    }

    static func makeForText() -> UILabel {
        let label = UILabel()
        label.font = .systemFont(ofSize: 16)
        label.textColor = .black
        label.numberOfLines = 0
        return label
    }
}

class ArticleViewController: UIViewController {
    lazy var titleLabel = UILabel.makeForTitle()
    lazy var textLabel = UILabel.makeForText()
}

#61 Child view controller auto-resizing

🧒 An awesome thing about child view controllers is that they're automatically resized to match their parent, making them a super nice solution for things like loading & error views.

class ListViewController: UIViewController {
    func loadItems() {
        let loadingViewController = LoadingViewController()
        add(loadingViewController)

        dataLoader.loadItems { [weak self] result in
            loadingViewController.remove()
            self?.handle(result)
        }
    }
}

For more about child view controller (including the add and remove methods used above), check out "Using child view controllers as plugins in Swift".

#60 Using zip

🤐 Using the zip function in Swift you can easily combine two sequences. Super useful when using two sequences to do some work, since zip takes care of all the bounds-checking.

func render(titles: [String]) {
    for (label, text) in zip(titleLabels, titles) {
        print(text)
        label.text = text
    }
}

#59 Defining custom option sets

🎛 The awesome thing about option sets in Swift is that they can automatically either be passed as a single member or as a set. Even cooler is that you can easily define your own option sets as well, perfect for options and other non-exclusive values.

// Option sets are awesome, because you can easily pass them
// both using dot syntax and array literal syntax, like when
// using the UIView animation API:
UIView.animate(withDuration: 0.3,
               delay: 0,
               options: .allowUserInteraction,
               animations: animations)

UIView.animate(withDuration: 0.3,
               delay: 0,
               options: [.allowUserInteraction, .layoutSubviews],
               animations: animations)

// The cool thing is that you can easily define your own option
// sets as well, by defining a struct that has an Int rawValue,
// that will be used as a bit mask.
extension Cache {
    struct Options: OptionSet {
        static let saveToDisk = Options(rawValue: 1)
        static let clearOnMemoryWarning = Options(rawValue: 1 << 1)
        static let clearDaily = Options(rawValue: 1 << 2)

        let rawValue: Int
    }
}

// We can now use Cache.Options just like UIViewAnimationOptions:
Cache(options: .saveToDisk)
Cache(options: [.saveToDisk, .clearDaily])

#58 Using the where clause with associated types

🙌 Using the where clause when designing protocol-oriented APIs in Swift can let your implementations (or others' if it's open source) have a lot more freedom, especially when it comes to collections.

See "Using generic type constraints in Swift 4" for more info.

public protocol PathFinderMap {
    associatedtype Node
    // Using the 'where' clause for associated types, we can
    // ensure that a type meets certain requirements (in this
    // case that it's a sequence with Node elements).
    associatedtype NodeSequence: Sequence where NodeSequence.Element == Node

    // Instead of using a concrete type (like [Node]) here, we
    // give implementors of this protocol more freedom while
    // still meeting our requirements. For example, one
    // implementation might use Set<Node>.
    func neighbors(of node: Node) -> NodeSequence
}

#57 Using first class functions when iterating over a dictionary

👨‍🍳 Combine first class functions in Swift with the fact that Dictionary elements are (Key, Value) tuples and you can build yourself some pretty awesome functional chains when iterating over a Dictionary.

func makeActor(at coordinate: Coordinate, for building: Building) -> Actor {
    let actor = Actor()
    actor.position = coordinate.point
    actor.animation = building.animation
    return actor
}

func render(_ buildings: [Coordinate : Building]) {
    buildings.map(makeActor).forEach(add)
}

#56 Calling instance methods as static functions

😎 In Swift, you can call any instance method as a static function and it will return a closure representing that method. This is how running tests using SPM on Linux works.

More about this topic in my blog post "First class functions in Swift".

// This produces a '() -> Void' closure which is a reference to the
// given view's 'removeFromSuperview' method.
let closure = UIView.removeFromSuperview(view)

// We can now call it just like we would any other closure, and it
// will run 'view.removeFromSuperview()'
closure()

// This is how running tests using the Swift Package Manager on Linux
// works, you return your test functions as closures:
extension UserManagerTests {
    static var allTests = [
        ("testLoggingIn", testLoggingIn),
        ("testLoggingOut", testLoggingOut),
        ("testUserPermissions", testUserPermissions)
    ]
}

#55 Dropping suffixes from method names to support multiple arguments

👏 One really nice benefit of dropping suffixes from method names (and just using verbs, when possible) is that it becomes super easy to support both single and multiple arguments, and it works really well semantically.

extension UIView {
    func add(_ subviews: UIView...) {
        subviews.forEach(addSubview)
    }
}

view.add(button)
view.add(label)

// By dropping the "Subview" suffix from the method name, both
// single and multiple arguments work really well semantically.
view.add(button, label)

#54 Constraining protocols to classes to ensure mutability

👽 Using the AnyObject (or class) constraint on protocols is not only useful when defining delegates (or other weak references), but also when you always want instances to be mutable without copying.

// By constraining a protocol with 'AnyObject' it can only be adopted
// by classes, which means all instances will always be mutable, and
// that it's the original instance (not a copy) that will be mutated.
protocol DataContainer: AnyObject {
    var data: Data? { get set }
}

class UserSettingsManager {
    private var settings: Settings
    private let dataContainer: DataContainer

    // Since DataContainer is a protocol, we an easily mock it in
    // tests if we use dependency injection
    init(settings: Settings, dataContainer: DataContainer) {
        self.settings = settings
        self.dataContainer = dataContainer
    }

    func saveSettings() throws {
        let data = try settings.serialize()

        // We can now assign properties on an instance of our protocol
        // because the compiler knows it's always going to be a class
        dataContainer.data = data
    }
}

#53 String-based enums in string interpolation

🍣 Even if you define a custom raw value for a string-based enum in Swift, the full case name will be used in string interpolation.

Super useful when using separate raw values for JSON, while still wanting to use the full case name in other contexts.

extension Building {
    // This enum has custom raw values that are used when decoding
    // a value, for example from JSON.
    enum Kind: String {
        case castle = "C"
        case town = "T"
        case barracks = "B"
        case goldMine = "G"
        case camp = "CA"
        case blacksmith = "BL"
    }

    var animation: Animation {
        return Animation(
            // When used in string interpolation, the full case name is still used.
            // For 'castle' this will be 'buildings/castle'.
            name: "buildings/\(kind)",
            frameCount: frameCount,
            frameDuration: frameDuration
        )
    }
}

#52 Expressively comparing a value with a list of candidates

👨‍🔬 Continuing to experiment with expressive ways of comparing a value with a list of candidates in Swift. Adding an extension on Equatable is probably my favorite approach so far.

extension Equatable {
    func isAny(of candidates: Self...) -> Bool {
        return candidates.contains(self)
    }
}

let isHorizontal = direction.isAny(of: .left, .right)

See tip #35 for my previous experiment.

#51 UIView bounds and transforms

📐 A really interesting side-effect of a UIView's bounds being its rect within its own coordinate system is that transforms don't affect it at all. That's why it's usually a better fit than frame when doing layout calculations of subviews.

let view = UIView()
view.frame.size = CGSize(width: 100, height: 100)
view.transform = CGAffineTransform(scaleX: 2, y: 2)

print(view.frame) // (-50.0, -50.0, 200.0, 200.0)
print(view.bounds) // (0.0, 0.0, 100.0, 100.0)

#50 UIKit default arguments

👏 It's awesome that many UIKit APIs with completion handlers and other optional parameters import into Swift with default arguments (even though they are written in Objective-C). Getting rid of all those nil arguments is so nice!

// BEFORE: All parameters are specified, just like in Objective-C

viewController.present(modalViewController, animated: true, completion: nil)

modalViewController.dismiss(animated: true, completion: nil)

viewController.transition(from: loadingViewController,
                          to: contentViewController,
                          duration: 0.3,
                          options: [],
                          animations: animations,
                          completion: nil)

// AFTER: Since many UIKit APIs with completion handlers and other
// optional parameters import into Swift with default arguments,
// we can make our calls shorter

viewController.present(modalViewController, animated: true)

modalViewController.dismiss(animated: true)

viewController.transition(from: loadingViewController,
                          to: contentViewController,
                          duration: 0.3,
                          animations: animations)

#49 Avoiding Massive View Controllers

✂️ Avoiding Massive View Controllers is all about finding the right levels of abstraction and splitting things up.

My personal rule of thumb is that as soon as I have 3 methods or properties that have the same prefix, I break them out into their own type.

// BEFORE

class LoginViewController: UIViewController {
    private lazy var signUpLabel = UILabel()
    private lazy var signUpImageView = UIImageView()
    private lazy var signUpButton = UIButton()
}

// AFTER

class LoginViewController: UIViewController {
    private lazy var signUpView = SignUpView()
}

class SignUpView: UIView {
    private lazy var label = UILabel()
    private lazy var imageView = UIImageView()
    private lazy var button = UIButton()
}

#48 Extending optionals

❤️ I love the fact that optionals are enums in Swift - it makes it so easy to extend them with convenience APIs for certain types. Especially useful when doing things like data validation on optional values.

func validateTextFields() -> Bool {
    guard !usernameTextField.text.isNilOrEmpty else {
        return false
    }

    ...

    return true
}

// Since all optionals are actual enum values in Swift, we can easily
// extend them for certain types, to add our own convenience APIs

extension Optional where Wrapped == String {
    var isNilOrEmpty: Bool {
        switch self {
        case let string?:
            return string.isEmpty
        case nil:
            return true
        }
    }
}

// Since strings are now Collections in Swift 4, you can even
// add this property to all optional collections:

extension Optional where Wrapped: Collection {
    var isNilOrEmpty: Bool {
        switch self {
        case let collection?:
            return collection.isEmpty
        case nil:
            return true
        }
    }
}

#47 Using where with for-loops

🗺 Using the where keyword can be a super nice way to quickly apply a filter in a for-loop in Swift. You can of course use map, filter and forEach, or guard, but for simple loops I think this is very expressive and nice.

func archiveMarkedPosts() {
    for post in posts where post.isMarked {
        archive(post)
    }
}

func healAllies() {
    for player in players where player.isAllied(to: currentPlayer) {
        player.heal()
    }
}

#46 Variable shadowing

👻 Variable shadowing can be super useful in Swift, especially when you want to create a local copy of a parameter value in order to use it as state within a closure.

init(repeatMode: RepeatMode, closure: @escaping () -> UpdateOutcome) {
    // Shadow the argument with a local, mutable copy
    var repeatMode = repeatMode
    
    self.closure = {
        // With shadowing, there's no risk of accidentially
        // referring to the immutable version
        switch repeatMode {
        case .forever:
            break
        case .times(let count):
            guard count > 0 else {
                return .finished
            }
            
            // We can now capture the mutable version and use
            // it for state in a closure
            repeatMode = .times(count - 1)
        }
        
        return closure()
    }
}

#45 Using dot syntax for static properties and initializers

✒️ Dot syntax is one of my favorite features of Swift. What's really cool is that it's not only for enums, any static method or property can be used with dot syntax - even initializers! Perfect for convenience APIs and default parameters.

public enum RepeatMode {
    case times(Int)
    case forever
}

public extension RepeatMode {
    static var never: RepeatMode {
        return .times(0)
    }

    static var once: RepeatMode {
        return .times(1)
    }
}

view.perform(animation, repeated: .once)

// To make default parameters more compact, you can even use init with dot syntax

class ImageLoader {
    init(cache: Cache = .init(), decoder: ImageDecoder = .init()) {
        ...
    }
}

#44 Calling functions as closures with a tuple as parameters

🚀 One really cool aspect of Swift having first class functions is that you can pass any function (or even initializer) as a closure, and even call it with a tuple containing its parameters!

// This function lets us treat any "normal" function or method as
// a closure and run it with a tuple that contains its parameters
func call<Input, Output>(_ function: (Input) -> Output, with input: Input) -> Output {
    return function(input)
}

class ViewFactory {
    func makeHeaderView() -> HeaderView {
        // We can now pass an initializer as a closure, and a tuple
        // containing its parameters
        return call(HeaderView.init, with: loadTextStyles())
    }
    
    private func loadTextStyles() -> (font: UIFont, color: UIColor) {
        return (theme.font, theme.textColor)
    }
}

class HeaderView {
    init(font: UIFont, textColor: UIColor) {
        ...
    }
}

#43 Enabling static dependency injection

💉 If you've been struggling to test code that uses static APIs, here's a technique you can use to enable static dependency injection without having to modify any call sites:

// Before: Almost impossible to test due to the use of singletons

class Analytics {
    static func log(_ event: Event) {
        Database.shared.save(event)
        
        let dictionary = event.serialize()
        NetworkManager.shared.post(dictionary, to: eventURL)
    }
}

// After: Much easier to test, since we can inject mocks as arguments

class Analytics {
    static func log(_ event: Event,
                    database: Database = .shared,
                    networkManager: NetworkManager = .shared) {
        database.save(event)
        
        let dictionary = event.serialize()
        networkManager.post(dictionary, to: eventURL)
    }
}

#42 Type inference for lazy properties in Swift 4

🎉 In Swift 4, type inference works for lazy properties and you don't need to explicitly refer to self!

// Swift 3

class PurchaseView: UIView {
    private lazy var buyButton: UIButton = self.makeBuyButton()
    
    private func makeBuyButton() -> UIButton {
        let button = UIButton()
        button.setTitle("Buy", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        return button
    }
}

// Swift 4

class PurchaseView: UIView {
    private lazy var buyButton = makeBuyButton()
    
    private func makeBuyButton() -> UIButton {
        let button = UIButton()
        button.setTitle("Buy", for: .normal)
        button.setTitleColor(.blue, for: .normal)
        return button
    }
}

#41 Converting Swift errors to NSError

😎 You can turn any Swift Error into an NSError, which is super useful when pattern matching with a code 👍. Also, switching on optionals is pretty cool!

let task = urlSession.dataTask(with: url) { data, _, error in
    switch error {
    case .some(let error as NSError) where error.code == NSURLErrorNotConnectedToInternet:
        presenter.showOfflineView()
    case .some(let error):
        presenter.showGenericErrorView()
    case .none:
        presenter.renderContent(from: data)
    }
}

task.resume()

Also make sure to check out Kostas Kremizas' tip about how you can pattern match directly against a member of URLError.

#40 Making UIImage macOS compatible

🖥 Here's an easy way to make iOS model code that uses UIImage macOS compatible - like me and Gui Rambo discussed on the Swift by Sundell Podcast.

// Either put this in a separate file that you only include in your macOS target or wrap the code in #if os(macOS) / #endif

import Cocoa

// Step 1: Typealias UIImage to NSImage
typealias UIImage = NSImage

// Step 2: You might want to add these APIs that UIImage has but NSImage doesn't.
extension NSImage {
    var cgImage: CGImage? {
        var proposedRect = CGRect(origin: .zero, size: size)

        return cgImage(forProposedRect: &proposedRect,
                       context: nil,
                       hints: nil)
    }

    convenience init?(named name: String) {
        self.init(named: Name(name))
    }
}

// Step 3: Profit - you can now make your model code that uses UIImage cross-platform!
struct User {
    let name: String
    let profileImage: UIImage
}

#39 Internally mutable protocol-oriented APIs

🤖 You can easily define a protocol-oriented API that can only be mutated internally, by using an internal protocol that extends a public one.

// Declare a public protocol that acts as your immutable API
public protocol ModelHolder {
    associatedtype Model
    var model: Model { get }
}

// Declare an extended, internal protocol that provides a mutable API
internal protocol MutableModelHolder: ModelHolder {
    var model: Model { get set }
}

// You can now implement the requirements using 'public internal(set)'
public class UserHolder: MutableModelHolder {
    public internal(set) var model: User

    internal init(model: User) {
        self.model = model
    }
}

#38 Switching on a set

🎛 You can switch on a set using array literals as cases in Swift! Can be really useful to avoid many if/else if statements.

class RoadTile: Tile {
    var connectedDirections = Set<Direction>()

    func render() {
        switch connectedDirections {
        case [.up, .down]:
            image = UIImage(named: "road-vertical")
        case [.left, .right]:
            image = UIImage(named: "road-horizontal")
        default:
            image = UIImage(named: "road")
        }
    }
}

#37 Adding the current locale to cache keys

🌍 When caching localized content in an app, it's a good idea to add the current locale to all keys, to prevent bugs when switching languages.

func cache(_ content: Content, forKey key: String) throws {
    let data = try wrap(content) as Data
    let key = localize(key: key)
    try storage.store(data, forKey: key)
}

func loadCachedContent(forKey key: String) -> Content? {
    let key = localize(key: key)
    let data = storage.loadData(forKey: key)
    return data.flatMap { try? unbox(data: $0) }
}

private func localize(key: String) -> String {
    return key + "-" + Bundle.main.preferredLocalizations[0]
}

#36 Setting up tests to avoid retain cycles with weak references

🚳 Here's an easy way to setup a test to avoid accidental retain cycles with object relationships (like weak delegates & observers) in Swift:

func testDelegateNotRetained() {
    // Assign the delegate (weak) and also retain it using a local var
    var delegate: Delegate? = DelegateMock()
    controller.delegate = delegate
    XCTAssertNotNil(controller.delegate)
    
    // Release the local var, which should also release the weak reference
    delegate = nil
    XCTAssertNil(controller.delegate)
}

#35 Expressively matching a value against a list of candidates

👨‍🔬 Playing around with an expressive way to check if a value matches any of a list of candidates in Swift:

// Instead of multiple conditions like this:

if string == "One" || string == "Two" || string == "Three" {

}

// You can now do:

if string == any(of: "One", "Two", "Three") {

}

You can find a gist with the implementation here.

#34 Organizing code using extensions

👪 APIs in a Swift extension automatically inherit its access control level, making it a neat way to organize public, internal & private APIs.

public extension Animation {
    init(textureNamed textureName: String) {
        frames = [Texture(name: textureName)]
    }
    
    init(texturesNamed textureNames: [String], frameDuration: TimeInterval = 1) {
        frames = textureNames.map(Texture.init)
        self.frameDuration = frameDuration
    }
    
    init(image: Image) {
        frames = [Texture(image: image)]
    }
}

internal extension Animation {
    func loadFrameImages() -> [Image] {
        return frames.map { $0.loadImageIfNeeded() }
    }
}

#33 Using map to transform an optional into a Result type

🗺 Using map you can transform an optional value into an optional Result type by simply passing in the enum case.

enum Result<Value> {
    case value(Value)
    case error(Error)
}

class Promise<Value> {
    private var result: Result<Value>?
    
    init(value: Value? = nil) {
        result = value.map(Result.value)
    }
}

#32 Assigning to self in struct initializers

👌 It's so nice that you can assign directly to self in struct initializers in Swift. Very useful when adding conformance to protocols.

extension Bool: AnswerConvertible {
    public init(input: String) throws {
        switch input.lowercased() {
        case "y", "yes", "👍":
            self = true
        default:
            self = false
        }
    }
}

#31 Recursively calling closures as inline functions

☎️ Defining Swift closures as inline functions enables you to recursively call them, which is super useful in things like custom sequences.

class Database {
    func records(matching query: Query) -> AnySequence<Record> {
        var recordIterator = loadRecords().makeIterator()
        
        func iterate() -> Record? {
            guard let nextRecord = recordIterator.next() else {
                return nil
            }
            
            guard nextRecord.matches(query) else {
                // Since the closure is an inline function, it can be recursively called,
                // in this case in order to advance to the next item.
                return iterate()
            }
            
            return nextRecord
        }
        
        // AnySequence/AnyIterator are part of the standard library and provide an easy way
        // to define custom sequences using closures.
        return AnySequence { AnyIterator(iterate) }
    }
}

Rob Napier points out that using the above might cause crashes if used on a large databaset, since Swift has no guaranteed Tail Call Optimization (TCO).

Slava Pestov also points out that another benefit of inline functions vs closures is that they can have their own generic parameter list.

#30 Passing self to required Objective-C dependencies

🏖 Using lazy properties in Swift, you can pass self to required Objective-C dependencies without having to use force-unwrapped optionals.

class DataLoader: NSObject {
    lazy var urlSession: URLSession = self.makeURLSession()
    
    private func makeURLSession() -> URLSession {
        return URLSession(configuration: .default, delegate: self, delegateQueue: .main)
    }
}

class Renderer {
    lazy var displayLink: CADisplayLink = self.makeDisplayLink()
    
    private func makeDisplayLink() -> CADisplayLink {
        return CADisplayLink(target: self, selector: #selector(screenDidRefresh))
    }
}

#29 Making weak or lazy properties readonly

👓 If you have a property in Swift that needs to be weak or lazy, you can still make it readonly by using private(set).

class Node {
    private(set) weak var parent: Node?
    private(set) lazy var children = [Node]()

    func add(child: Node) {
        children.append(child)
        child.parent = self
    }
}

#28 Defining static URLs using string literals

🌏 Tired of using URL(string: "url")! for static URLs? Make URL conform to ExpressibleByStringLiteral and you can now simply use "url" instead.

extension URL: ExpressibleByStringLiteral {
    // By using 'StaticString' we disable string interpolation, for safety
    public init(stringLiteral value: StaticString) {
        self = URL(string: "\(value)").require(hint: "Invalid URL string literal: \(value)")
    }
}

// We can now define URLs using static string literals 🎉
let url: URL = "https://www.swiftbysundell.com"
let task = URLSession.shared.dataTask(with: "https://www.swiftbysundell.com")

// In Swift 3 or earlier, you also have to implement 2 additional initializers
extension URL {
    public init(extendedGraphemeClusterLiteral value: StaticString) {
        self.init(stringLiteral: value)
    }

    public init(unicodeScalarLiteral value: StaticString) {
        self.init(stringLiteral: value)
    }
}

To find the extension that adds the require() method on Optional that I use above, check out Require.

#27 Manipulating points, sizes and frames using math operators

✚ I'm always careful with operator overloading, but for manipulating things like sizes, points & frames I find them super useful.

extension CGSize {
    static func *(lhs: CGSize, rhs: CGFloat) -> CGSize {
        return CGSize(width: lhs.width * rhs, height: lhs.height * rhs)
    }
}

button.frame.size = image.size * 2

If you like the above idea, check out CGOperators, which contains math operator overloads for all Core Graphics' vector types.

#26 Using closure types in generic constraints

🔗 You can use closure types in generic constraints in Swift. Enables nice APIs for handling sequences of closures.

extension Sequence where Element == () -> Void {
    func callAll() {
        forEach { $0() }
    }
}

extension Sequence where Element == () -> String {
    func joinedResults(separator: String) -> String {
        return map { $0() }.joined(separator: separator)
    }
}

callbacks.callAll()
let names = nameProviders.joinedResults(separator: ", ")

(If you're using Swift 3, you have to change Element to Iterator.Element)

#25 Using associated enum values to avoid state-specific optionals

🎉 Using associated enum values is a super nice way to encapsulate mutually exclusive state info (and avoiding state-specific optionals).

// BEFORE: Lots of state-specific, optional properties

class Player {
    var isWaitingForMatchMaking: Bool
    var invitingUser: User?
    var numberOfLives: Int
    var playerDefeatedBy: Player?
    var roundDefeatedIn: Int?
}

// AFTER: All state-specific information is encapsulated in enum cases

class Player {
    enum State {
        case waitingForMatchMaking
        case waitingForInviteResponse(from: User)
        case active(numberOfLives: Int)
        case defeated(by: Player, roundNumber: Int)
    }
    
    var state: State
}

#24 Using enums for async result types

👍 I really like using enums for all async result types, even boolean ones. Self-documenting, and makes the call site a lot nicer to read too!

protocol PushNotificationService {
    // Before
    func enablePushNotifications(completionHandler: @escaping (Bool) -> Void)
    
    // After
    func enablePushNotifications(completionHandler: @escaping (PushNotificationStatus) -> Void)
}

enum PushNotificationStatus {
    case enabled
    case disabled
}

service.enablePushNotifications { status in
    if status == .enabled {
        enableNotificationsButton.removeFromSuperview()
    }
}

#23 Working on async code in a playground

🏃 Want to work on your async code in a Swift Playground? Just set needsIndefiniteExecution to true to keep it running:

import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true

DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
    let greeting = "Hello after 3 seconds"
    print(greeting)
}

To stop the playground from executing, simply call PlaygroundPage.current.finishExecution().

#22 Overriding self with a weak reference

💦 Avoid memory leaks when accidentially refering to self in closures by overriding it locally with a weak reference:

Swift >= 4.2

dataLoader.loadData(from: url) { [weak self] result in
    guard let self = self else { 
        return 
    }

    self.cache(result)
    
    ...

Swift < 4.2

dataLoader.loadData(from: url) { [weak self] result in
    guard let `self` = self else {
        return
    }

    self.cache(result)
    
    ...

Note that the reason the above currently works is because of a compiler bug (which I hope gets turned into a properly supported feature soon).

#21 Using DispatchWorkItem

🕓 Using dispatch work items you can easily cancel a delayed asynchronous GCD task if you no longer need it:

let workItem = DispatchWorkItem {
    // Your async code goes in here
}

// Execute the work item after 1 second
DispatchQueue.main.asyncAfter(deadline: .now() + 1, execute: workItem)

// You can cancel the work item if you no longer need it
workItem.cancel()

#20 Combining a sequence of functions

➕ While working on a new Swift developer tool (to be open sourced soon 😉), I came up with a pretty neat way of organizing its sequence of operations, by combining their functions into a closure:

internal func +<A, B, C>(lhs: @escaping (A) throws -> B,
                         rhs: @escaping (B) throws -> C) -> (A) throws -> C {
    return { try rhs(lhs($0)) }
}

public func run() throws {
    try (determineTarget + build + analyze + output)()
}

If you're familiar with the functional programming world, you might know the above technique as the pipe operator (thanks to Alexey Demedreckiy for pointing this out!)

#19 Chaining optionals with map() and flatMap()

🗺 Using map() and flatMap() on optionals you can chain multiple operations without having to use lengthy if lets or guards:

// BEFORE

guard let string = argument(at: 1) else {
    return
}

guard let url = URL(string: string) else {
    return
}

handle(url)

// AFTER

argument(at: 1).flatMap(URL.init).map(handle)

#18 Using self-executing closures for lazy properties

🚀 Using self-executing closures is a great way to encapsulate lazy property initialization:

class StoreViewController: UIViewController {
    private lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        let view = UICollectionView(frame: self.view.bounds, collectionViewLayout: layout)
        view.delegate = self
        view.dataSource = self
        return view
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(collectionView)
    }
}

#17 Speeding up Swift package tests

⚡️ You can speed up your Swift package tests using the --parallel flag. For Marathon, the tests execute 3 times faster that way!

swift test --parallel

#16 Avoiding mocking UserDefaults

🛠 Struggling with mocking UserDefaults in a test? The good news is: you don't need mocking - just create a real instance:

class LoginTests: XCTestCase {
    private var userDefaults: UserDefaults!
    private var manager: LoginManager!
    
    override func setUp() {
        super.setup()
        
        userDefaults = UserDefaults(suiteName: #file)
        userDefaults.removePersistentDomain(forName: #file)
        
        manager = LoginManager(userDefaults: userDefaults)
    }
}

#15 Using variadic parameters

👍 Using variadic parameters in Swift, you can create some really nice APIs that take a list of objects without having to use an array:

extension Canvas {
    func add(_ shapes: Shape...) {
        shapes.forEach(add)
    }
}

let circle = Circle(center: CGPoint(x: 5, y: 5), radius: 5)
let lineA = Line(start: .zero, end: CGPoint(x: 10, y: 10))
let lineB = Line(start: CGPoint(x: 0, y: 10), end: CGPoint(x: 10, y: 0))

let canvas = Canvas()
canvas.add(circle, lineA, lineB)
canvas.render()

#14 Referring to enum cases with associated values as closures

😮 Just like you can refer to a Swift function as a closure, you can do the same thing with enum cases with associated values:

enum UnboxPath {
    case key(String)
    case keyPath(String)
}

struct UserSchema {
    static let name = key("name")
    static let age = key("age")
    static let posts = key("posts")
    
    private static let key = UnboxPath.key
}

#13 Using the === operator to compare objects by instance

📈 The === operator lets you check if two objects are the same instance. Very useful when verifying that an array contains an instance in a test:

protocol InstanceEquatable: class, Equatable {}

extension InstanceEquatable {
    static func ==(lhs: Self, rhs: Self) -> Bool {
        return lhs === rhs
    }
}

extension Enemy: InstanceEquatable {}

func testDestroyingEnemy() {
    player.attack(enemy)
    XCTAssertTrue(player.destroyedEnemies.contains(enemy))
}

#12 Calling initializers with dot syntax and passing them as closures

😎 Cool thing about Swift initializers: you can call them using dot syntax and pass them as closures! Perfect for mocking dates in tests.

class Logger {
    private let storage: LogStorage
    private let dateProvider: () -> Date
    
    init(storage: LogStorage = .init(), dateProvider: @escaping () -> Date = Date.init) {
        self.storage = storage
        self.dateProvider = dateProvider
    }
    
    func log(event: Event) {
        storage.store(event: event, date: dateProvider())
    }
}

#11 Structuring UI tests as extensions on XCUIApplication

📱 Most of my UI testing logic is now categories on XCUIApplication. Makes the test cases really easy to read:

func testLoggingInAndOut() {
    XCTAssertFalse(app.userIsLoggedIn)
    
    app.launch()
    app.login()
    XCTAssertTrue(app.userIsLoggedIn)
    
    app.logout()
    XCTAssertFalse(app.userIsLoggedIn)
}

func testDisplayingCategories() {
    XCTAssertFalse(app.isDisplayingCategories)
    
    app.launch()
    app.login()
    app.goToCategories()
    XCTAssertTrue(app.isDisplayingCategories)
}

#10 Avoiding default cases in switch statements

🙂 It’s a good idea to avoid “default” cases when switching on Swift enums - it’ll “force you” to update your logic when a new case is added:

enum State {
    case loggedIn
    case loggedOut
    case onboarding
}

func handle(_ state: State) {
    switch state {
    case .loggedIn:
        showMainUI()
    case .loggedOut:
        showLoginUI()
    // Compiler error: Switch must be exhaustive
    }
}

#9 Using the guard statement in many different scopes

💂 It's really cool that you can use Swift's 'guard' statement to exit out of pretty much any scope, not only return from functions:

// You can use the 'guard' statement to...

for string in strings {
    // ...continue an iteration
    guard shouldProcess(string) else {
        continue
    }
    
    // ...or break it
    guard !shouldBreak(for: string) else {
        break
    }
    
    // ...or return
    guard !shouldReturn(for: string) else {
        return
    }
    
    // ..or throw an error
    guard string.isValid else {
        throw StringError.invalid(string)
    }
    
    // ...or exit the program
    guard !shouldExit(for: string) else {
        exit(1)
    }
}

#8 Passing functions & operators as closures

❤️ Love how you can pass functions & operators as closures in Swift. For example, it makes the syntax for sorting arrays really nice!

let array = [3, 9, 1, 4, 6, 2]
let sorted = array.sorted(by: <)

#7 Using #function for UserDefaults key consistency

🗝 Here's a neat little trick I use to get UserDefault key consistency in Swift (#function expands to the property name in getters/setters). Just remember to write a good suite of tests that'll guard you against bugs when changing property names.

extension UserDefaults {
    var onboardingCompleted: Bool {
        get { return bool(forKey: #function) }
        set { set(newValue, forKey: #function) }
    }
}

#6 Using a name already taken by the standard library

📛 Want to use a name already taken by the standard library for a nested type? No problem - just use Swift. to disambiguate:

extension Command {
    enum Error: Swift.Error {
        case missing
        case invalid(String)
    }
}

#5 Using Wrap to implement Equatable

📦 Playing around with using Wrap to implement Equatable for any type, primarily for testing:

protocol AutoEquatable: Equatable {}

extension AutoEquatable {
    static func ==(lhs: Self, rhs: Self) -> Bool {
        let lhsData = try! wrap(lhs) as Data
        let rhsData = try! wrap(rhs) as Data
        return lhsData == rhsData
    }
}

#4 Using typealiases to reduce the length of method signatures

📏 One thing that I find really useful in Swift is to use typealiases to reduce the length of method signatures in generic types:

public class PathFinder<Object: PathFinderObject> {
    public typealias Map = Object.Map
    public typealias Node = Map.Node
    public typealias Path = PathFinderPath<Object>
    
    public static func possiblePaths(for object: Object, at rootNode: Node, on map: Map) -> Path.Sequence {
        return .init(object: object, rootNode: rootNode, map: map)
    }
}

#3 Referencing either external or internal parameter name when writing docs

📖 You can reference either the external or internal parameter label when writing Swift docs - and they get parsed the same:

// EITHER:

class Foo {
    /**
    *   - parameter string: A string
    */
    func bar(with string: String) {}
}

// OR:

class Foo {
    /**
    *   - parameter with: A string
    */
    func bar(with string: String) {}
}

#2 Using auto closures

👍 Finding more and more uses for auto closures in Swift. Can enable some pretty nice APIs:

extension Dictionary {
    mutating func value(for key: Key, orAdd valueClosure: @autoclosure () -> Value) -> Value {
        if let value = self[key] {
            return value
        }
        
        let value = valueClosure()
        self[key] = value
        return value
    }
}

#1 Namespacing with nested types

🚀 I’ve started to become a really big fan of nested types in Swift. Love the additional namespacing it gives you!

public struct Map {
    public struct Model {
        public let size: Size
        public let theme: Theme
        public var terrain: [Position : Terrain.Model]
        public var units: [Position : Unit.Model]
        public var buildings: [Position : Building.Model]
    }
    
    public enum Direction {
        case up
        case right
        case down
        case left
    }
    
    public struct Position {
        public var x: Int
        public var y: Int
    }
    
    public enum Size: String {
        case small = "S"
        case medium = "M"
        case large = "L"
        case extraLarge = "XL"
    }
}

Download Details:

Author: JohnSundell
Source code: https://github.com/JohnSundell/SwiftTips

License: MIT license
#swift

Francesco Nicolas

1646698200

Face Recognition with OpenCV and Python

Introduction

What is face recognition? Or what is recognition? When you look at an apple fruit, your mind immediately tells you that this is an apple fruit. This process, your mind telling you that this is an apple fruit is recognition in simple words. So what is face recognition then? I am sure you have guessed it right. When you look at your friend walking down the street or a picture of him, you recognize that he is your friend Paulo. Interestingly when you look at your friend or a picture of him you look at his face first before looking at anything else. Ever wondered why you do that? This is so that you can recognize him by looking at his face. Well, this is you doing face recognition.

But the real question is how does face recognition works? It is quite simple and intuitive. Take a real life example, when you meet someone first time in your life you don't recognize him, right? While he talks or shakes hands with you, you look at his face, eyes, nose, mouth, color and overall look. This is your mind learning or training for the face recognition of that person by gathering face data. Then he tells you that his name is Paulo. At this point your mind knows that the face data it just learned belongs to Paulo. Now your mind is trained and ready to do face recognition on Paulo's face. Next time when you will see Paulo or his face in a picture you will immediately recognize him. This is how face recognition work. The more you will meet Paulo, the more data your mind will collect about Paulo and especially his face and the better you will become at recognizing him.

Now the next question is how to code face recognition with OpenCV, after all this is the only reason why you are reading this article, right? OK then. You might say that our mind can do these things easily but to actually code them into a computer is difficult? Don't worry, it is not. Thanks to OpenCV, coding face recognition is as easier as it feels. The coding steps for face recognition are same as we discussed it in real life example above.

Training Data Gathering: Gather face data (face images in this case) of the persons you want to recognize
Training of Recognizer: Feed that face data (and respective names of each face) to the face recognizer so that it can learn.
Recognition: Feed new faces of the persons and see if the face recognizer you just trained recognizes them.

OpenCV comes equipped with built in face recognizer, all you have to do is feed it the face data. It's that simple and this how it will look once we are done coding it.

visualization

OpenCV Face Recognizers

OpenCV has three built in face recognizers and thanks to OpenCV's clean coding, you can use any of them by just changing a single line of code. Below are the names of those face recognizers and their OpenCV calls.

EigenFaces Face Recognizer Recognizer - cv2.face.createEigenFaceRecognizer()
FisherFaces Face Recognizer Recognizer - cv2.face.createFisherFaceRecognizer()
Local Binary Patterns Histograms (LBPH) Face Recognizer - cv2.face.createLBPHFaceRecognizer()

We have got three face recognizers but do you know which one to use and when? Or which one is better? I guess not. So why not go through a brief summary of each, what you say? I am assuming you said yes :) So let's dive into the theory of each.

EigenFaces Face Recognizer

This algorithm considers the fact that not all parts of a face are equally important and equally useful. When you look at some one you recognize him/her by his distinct features like eyes, nose, cheeks, forehead and how they vary with respect to each other. So you are actually focusing on the areas of maximum change (mathematically speaking, this change is variance) of the face. For example, from eyes to nose there is a significant change and same is the case from nose to mouth. When you look at multiple faces you compare them by looking at these parts of the faces because these parts are the most useful and important components of a face. Important because they catch the maximum change among faces, change the helps you differentiate one face from the other. This is exactly how EigenFaces face recognizer works.

EigenFaces face recognizer looks at all the training images of all the persons as a whole and try to extract the components which are important and useful (the components that catch the maximum variance/change) and discards the rest of the components. This way it not only extracts the important components from the training data but also saves memory by discarding the less important components. These important components it extracts are called principal components. Below is an image showing the principal components extracted from a list of faces.

Principal Components eigenfaces_opencv source

You can see that principal components actually represent faces and these faces are called eigen faces and hence the name of the algorithm.

So this is how EigenFaces face recognizer trains itself (by extracting principal components). Remember, it also keeps a record of which principal component belongs to which person. One thing to note in above image is that Eigenfaces algorithm also considers illumination as an important component.

Later during recognition, when you feed a new image to the algorithm, it repeats the same process on that image as well. It extracts the principal component from that new image and compares that component with the list of components it stored during training and finds the component with the best match and returns the person label associated with that best match component.

Easy peasy, right? Next one is easier than this one.

FisherFaces Face Recognizer

This algorithm is an improved version of EigenFaces face recognizer. Eigenfaces face recognizer looks at all the training faces of all the persons at once and finds principal components from all of them combined. By capturing principal components from all the of them combined you are not focusing on the features that discriminate one person from the other but the features that represent all the persons in the training data as a whole.

This approach has drawbacks, for example, images with sharp changes (like light changes which is not a useful feature at all) may dominate the rest of the images and you may end up with features that are from external source like light and are not useful for discrimination at all. In the end, your principal components will represent light changes and not the actual face features.

Fisherfaces algorithm, instead of extracting useful features that represent all the faces of all the persons, it extracts useful features that discriminate one person from the others. This way features of one person do not dominate over the others and you have the features that discriminate one person from the others.

Below is an image of features extracted using Fisherfaces algorithm.

Fisher Faces eigenfaces_opencv source

You can see that features extracted actually represent faces and these faces are called fisher faces and hence the name of the algorithm.

One thing to note here is that even in Fisherfaces algorithm if multiple persons have images with sharp changes due to external sources like light they will dominate over other features and affect recognition accuracy.

Getting bored with this theory? Don't worry, only one face recognizer is left and then we will dive deep into the coding part.

Local Binary Patterns Histograms (LBPH) Face Recognizer

I wrote a detailed explaination on Local Binary Patterns Histograms in my previous article on face detection using local binary patterns histograms. So here I will just give a brief overview of how it works.

We know that Eigenfaces and Fisherfaces are both affected by light and in real life we can't guarantee perfect light conditions. LBPH face recognizer is an improvement to overcome this drawback.

Idea is to not look at the image as a whole instead find the local features of an image. LBPH alogrithm try to find the local structure of an image and it does that by comparing each pixel with its neighboring pixels.

Take a 3x3 window and move it one image, at each move (each local part of an image), compare the pixel at the center with its neighbor pixels. The neighbors with intensity value less than or equal to center pixel are denoted by 1 and others by 0. Then you read these 0/1 values under 3x3 window in a clockwise order and you will have a binary pattern like 11100011 and this pattern is local to some area of the image. You do this on whole image and you will have a list of local binary patterns.

LBP Labeling

Now you get why this algorithm has Local Binary Patterns in its name? Because you get a list of local binary patterns. Now you may be wondering, what about the histogram part of the LBPH? Well after you get a list of local binary patterns, you convert each binary pattern into a decimal number (as shown in above image) and then you make a histogram of all of those values. A sample histogram looks like this.

Sample Histogram LBP labeling

I guess this answers the question about histogram part. So in the end you will have one histogram for each face image in the training data set. That means if there were 100 images in training data set then LBPH will extract 100 histograms after training and store them for later recognition. Remember, algorithm also keeps track of which histogram belongs to which person.

Later during recognition, when you will feed a new image to the recognizer for recognition it will generate a histogram for that new image, compare that histogram with the histograms it already has, find the best match histogram and return the person label associated with that best match histogram.

Below is a list of faces and their respective local binary patterns images. You can see that the LBP images are not affected by changes in light conditions.

LBP Faces source

The theory part is over and now comes the coding part! Ready to dive into coding? Let's get into it then.

Coding Face Recognition with OpenCV

The Face Recognition process in this tutorial is divided into three steps.

Prepare training data: In this step we will read training images for each person/subject along with their labels, detect faces from each image and assign each detected face an integer label of the person it belongs to.
Train Face Recognizer: In this step we will train OpenCV's LBPH face recognizer by feeding it the data we prepared in step 1.
Testing: In this step we will pass some test images to face recognizer and see if it predicts them correctly.

[There should be a visualization diagram for above steps here]

To detect faces, I will use the code from my previous article on face detection. So if you have not read it, I encourage you to do so to understand how face detection works and its Python coding.

Import Required Modules

Before starting the actual coding we need to import the required modules for coding. So let's import them first.

cv2: is OpenCV module for Python which we will use for face detection and face recognition.
os: We will use this Python module to read our training directories and file names.
numpy: We will use this module to convert Python lists to numpy arrays as OpenCV face recognizers accept numpy arrays.

#import OpenCV module
import cv2
#import os module for reading training data directories and paths
import os
#import numpy to convert python lists to numpy arrays as 
#it is needed by OpenCV face recognizers
import numpy as np

#matplotlib for display our images
import matplotlib.pyplot as plt
%matplotlib inline

Training Data

The more images used in training the better. Normally a lot of images are used for training a face recognizer so that it can learn different looks of the same person, for example with glasses, without glasses, laughing, sad, happy, crying, with beard, without beard etc. To keep our tutorial simple we are going to use only 12 images for each person.

So our training data consists of total 2 persons with 12 images of each person. All training data is inside training-data folder. training-data folder contains one folder for each person and each folder is named with format sLabel (e.g. s1, s2) where label is actually the integer label assigned to that person. For example folder named s1 means that this folder contains images for person 1. The directory structure tree for training data is as follows:

training-data
|-------------- s1
|               |-- 1.jpg
|               |-- ...
|               |-- 12.jpg
|-------------- s2
|               |-- 1.jpg
|               |-- ...
|               |-- 12.jpg

The test-data folder contains images that we will use to test our face recognizer after it has been successfully trained.

As OpenCV face recognizer accepts labels as integers so we need to define a mapping between integer labels and persons actual names so below I am defining a mapping of persons integer labels and their respective names.

Note: As we have not assigned label 0 to any person so the mapping for label 0 is empty.

#there is no label 0 in our training data so subject name for index/label 0 is empty
subjects = ["", "Tom Cruise", "Shahrukh Khan"]

Prepare training data

You may be wondering why data preparation, right? Well, OpenCV face recognizer accepts data in a specific format. It accepts two vectors, one vector is of faces of all the persons and the second vector is of integer labels for each face so that when processing a face the face recognizer knows which person that particular face belongs too.

For example, if we had 2 persons and 2 images for each person.

PERSON-1    PERSON-2   

img1        img1         
img2        img2

Then the prepare data step will produce following face and label vectors.

FACES                        LABELS

person1_img1_face              1
person1_img2_face              1
person2_img1_face              2
person2_img2_face              2

Preparing data step can be further divided into following sub-steps.

Read all the folder names of subjects/persons provided in training data folder. So for example, in this tutorial we have folder names: s1, s2.
For each subject, extract label number. Do you remember that our folders have a special naming convention? Folder names follow the format sLabel where Label is an integer representing the label we have assigned to that subject. So for example, folder name s1 means that the subject has label 1, s2 means subject label is 2 and so on. The label extracted in this step is assigned to each face detected in the next step.
Read all the images of the subject, detect face from each image.
Add each face to faces vector with corresponding subject label (extracted in above step) added to labels vector.

[There should be a visualization for above steps here]

Did you read my last article on face detection? No? Then you better do so right now because to detect faces, I am going to use the code from my previous article on face detection. So if you have not read it, I encourage you to do so to understand how face detection works and its coding. Below is the same code.

#function to detect face using OpenCV
def detect_face(img):
    #convert the test image to gray image as opencv face detector expects gray images
    gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
    
    #load OpenCV face detector, I am using LBP which is fast
    #there is also a more accurate but slow Haar classifier
    face_cascade = cv2.CascadeClassifier('opencv-files/lbpcascade_frontalface.xml')

    #let's detect multiscale (some images may be closer to camera than others) images
    #result is a list of faces
    faces = face_cascade.detectMultiScale(gray, scaleFactor=1.2, minNeighbors=5);
    
    #if no faces are detected then return original img
    if (len(faces) == 0):
        return None, None
    
    #under the assumption that there will be only one face,
    #extract the face area
    (x, y, w, h) = faces[0]
    
    #return only the face part of the image
    return gray[y:y+w, x:x+h], faces[0]

I am using OpenCV's LBP face detector. On line 4, I convert the image to grayscale because most operations in OpenCV are performed in gray scale, then on line 8 I load LBP face detector using cv2.CascadeClassifier class. After that on line 12 I use cv2.CascadeClassifier class' detectMultiScale method to detect all the faces in the image. on line 20, from detected faces I only pick the first face because in one image there will be only one face (under the assumption that there will be only one prominent face). As faces returned by detectMultiScale method are actually rectangles (x, y, width, height) and not actual faces images so we have to extract face image area from the main image. So on line 23 I extract face area from gray image and return both the face image area and face rectangle.

Now you have got a face detector and you know the 4 steps to prepare the data, so are you ready to code the prepare data step? Yes? So let's do it.

#this function will read all persons' training images, detect face from each image
#and will return two lists of exactly same size, one list 
# of faces and another list of labels for each face
def prepare_training_data(data_folder_path):
    
    #------STEP-1--------
    #get the directories (one directory for each subject) in data folder
    dirs = os.listdir(data_folder_path)
    
    #list to hold all subject faces
    faces = []
    #list to hold labels for all subjects
    labels = []
    
    #let's go through each directory and read images within it
    for dir_name in dirs:
        
        #our subject directories start with letter 's' so
        #ignore any non-relevant directories if any
        if not dir_name.startswith("s"):
            continue;
            
        #------STEP-2--------
        #extract label number of subject from dir_name
        #format of dir name = slabel
        #, so removing letter 's' from dir_name will give us label
        label = int(dir_name.replace("s", ""))
        
        #build path of directory containin images for current subject subject
        #sample subject_dir_path = "training-data/s1"
        subject_dir_path = data_folder_path + "/" + dir_name
        
        #get the images names that are inside the given subject directory
        subject_images_names = os.listdir(subject_dir_path)
        
        #------STEP-3--------
        #go through each image name, read image, 
        #detect face and add face to list of faces
        for image_name in subject_images_names:
            
            #ignore system files like .DS_Store
            if image_name.startswith("."):
                continue;
            
            #build image path
            #sample image path = training-data/s1/1.pgm
            image_path = subject_dir_path + "/" + image_name

            #read image
            image = cv2.imread(image_path)
            
            #display an image window to show the image 
            cv2.imshow("Training on image...", image)
            cv2.waitKey(100)
            
            #detect face
            face, rect = detect_face(image)
            
            #------STEP-4--------
            #for the purpose of this tutorial
            #we will ignore faces that are not detected
            if face is not None:
                #add face to list of faces
                faces.append(face)
                #add label for this face
                labels.append(label)
            
    cv2.destroyAllWindows()
    cv2.waitKey(1)
    cv2.destroyAllWindows()
    
    return faces, labels

I have defined a function that takes the path, where training subjects' folders are stored, as parameter. This function follows the same 4 prepare data substeps mentioned above.

(step-1) On line 8 I am using os.listdir method to read names of all folders stored on path passed to function as parameter. On line 10-13 I am defining labels and faces vectors.

(step-2) After that I traverse through all subjects' folder names and from each subject's folder name on line 27 I am extracting the label information. As folder names follow the sLabel naming convention so removing the letter s from folder name will give us the label assigned to that subject.

(step-3) On line 34, I read all the images names of of the current subject being traversed and on line 39-66 I traverse those images one by one. On line 53-54 I am using OpenCV's imshow(window_title, image) along with OpenCV's waitKey(interval) method to display the current image being traveresed. The waitKey(interval) method pauses the code flow for the given interval (milliseconds), I am using it with 100ms interval so that we can view the image window for 100ms. On line 57, I detect face from the current image being traversed.

(step-4) On line 62-66, I add the detected face and label to their respective vectors.

But a function can't do anything unless we call it on some data that it has to prepare, right? Don't worry, I have got data of two beautiful and famous celebrities. I am sure you will recognize them!

training-data

Let's call this function on images of these beautiful celebrities to prepare data for training of our Face Recognizer. Below is a simple code to do that.

#let's first prepare our training data
#data will be in two lists of same size
#one list will contain all the faces
#and other list will contain respective labels for each face
print("Preparing data...")
faces, labels = prepare_training_data("training-data")
print("Data prepared")

#print total faces and labels
print("Total faces: ", len(faces))
print("Total labels: ", len(labels))

Preparing data...
Data prepared
Total faces:  23
Total labels:  23

This was probably the boring part, right? Don't worry, the fun stuff is coming up next. It's time to train our own face recognizer so that once trained it can recognize new faces of the persons it was trained on. Read? Ok then let's train our face recognizer.

Train Face Recognizer

As we know, OpenCV comes equipped with three face recognizers.

EigenFace Recognizer: This can be created with cv2.face.createEigenFaceRecognizer()
FisherFace Recognizer: This can be created with cv2.face.createFisherFaceRecognizer()
Local Binary Patterns Histogram (LBPH): This can be created with cv2.face.LBPHFisherFaceRecognizer()

I am going to use LBPH face recognizer but you can use any face recognizer of your choice. No matter which of the OpenCV's face recognizer you use the code will remain the same. You just have to change one line, the face recognizer initialization line given below.

#create our LBPH face recognizer 
face_recognizer = cv2.face.createLBPHFaceRecognizer()

#or use EigenFaceRecognizer by replacing above line with 
#face_recognizer = cv2.face.createEigenFaceRecognizer()

#or use FisherFaceRecognizer by replacing above line with 
#face_recognizer = cv2.face.createFisherFaceRecognizer()

Now that we have initialized our face recognizer and we also have prepared our training data, it's time to train the face recognizer. We will do that by calling the train(faces-vector, labels-vector) method of face recognizer.

#train our face recognizer of our training faces
face_recognizer.train(faces, np.array(labels))

Did you notice that instead of passing labels vector directly to face recognizer I am first converting it to numpy array? This is because OpenCV expects labels vector to be a numpy array.

Still not satisfied? Want to see some action? Next step is the real action, I promise!

Prediction

Now comes my favorite part, the prediction part. This is where we actually get to see if our algorithm is actually recognizing our trained subjects's faces or not. We will take two test images of our celeberities, detect faces from each of them and then pass those faces to our trained face recognizer to see if it recognizes them.

Below are some utility functions that we will use for drawing bounding box (rectangle) around face and putting celeberity name near the face bounding box.

#function to draw rectangle on image 
#according to given (x, y) coordinates and 
#given width and heigh
def draw_rectangle(img, rect):
    (x, y, w, h) = rect
    cv2.rectangle(img, (x, y), (x+w, y+h), (0, 255, 0), 2)
    
#function to draw text on give image starting from
#passed (x, y) coordinates. 
def draw_text(img, text, x, y):
    cv2.putText(img, text, (x, y), cv2.FONT_HERSHEY_PLAIN, 1.5, (0, 255, 0), 2)

First function draw_rectangle draws a rectangle on image based on passed rectangle coordinates. It uses OpenCV's built in function cv2.rectangle(img, topLeftPoint, bottomRightPoint, rgbColor, lineWidth) to draw rectangle. We will use it to draw a rectangle around the face detected in test image.

Second function draw_text uses OpenCV's built in function cv2.putText(img, text, startPoint, font, fontSize, rgbColor, lineWidth) to draw text on image.

Now that we have the drawing functions, we just need to call the face recognizer's predict(face) method to test our face recognizer on test images. Following function does the prediction for us.

#this function recognizes the person in image passed
#and draws a rectangle around detected face with name of the 
#subject
def predict(test_img):
    #make a copy of the image as we don't want to chang original image
    img = test_img.copy()
    #detect face from the image
    face, rect = detect_face(img)

    #predict the image using our face recognizer 
    label= face_recognizer.predict(face)
    #get name of respective label returned by face recognizer
    label_text = subjects[label]
    
    #draw a rectangle around face detected
    draw_rectangle(img, rect)
    #draw name of predicted person
    draw_text(img, label_text, rect[0], rect[1]-5)
    
    return img

line-6 read the test image
line-7 detect face from test image
line-11 recognize the face by calling face recognizer's predict(face) method. This method will return a lable
line-12 get the name associated with the label
line-16 draw rectangle around the detected face
line-18 draw name of predicted subject above face rectangle

Now that we have the prediction function well defined, next step is to actually call this function on our test images and display those test images to see if our face recognizer correctly recognized them. So let's do it. This is what we have been waiting for.

print("Predicting images...")

#load test images
test_img1 = cv2.imread("test-data/test1.jpg")
test_img2 = cv2.imread("test-data/test2.jpg")

#perform a prediction
predicted_img1 = predict(test_img1)
predicted_img2 = predict(test_img2)
print("Prediction complete")

#create a figure of 2 plots (one for each test image)
f, (ax1, ax2) = plt.subplots(1, 2, figsize=(10, 5))

#display test image1 result
ax1.imshow(cv2.cvtColor(predicted_img1, cv2.COLOR_BGR2RGB))

#display test image2 result
ax2.imshow(cv2.cvtColor(predicted_img2, cv2.COLOR_BGR2RGB))

#display both images
cv2.imshow("Tom cruise test", predicted_img1)
cv2.imshow("Shahrukh Khan test", predicted_img2)
cv2.waitKey(0)
cv2.destroyAllWindows()
cv2.waitKey(1)
cv2.destroyAllWindows()

Predicting images...
Prediction complete

wohooo! Is'nt it beautiful? Indeed, it is!

End Notes

Face Recognition is a fascinating idea to work on and OpenCV has made it extremely simple and easy for us to code it. It just takes a few lines of code to have a fully working face recognition application and we can switch between all three face recognizers with a single line of code change. It's that simple.

Although EigenFaces, FisherFaces and LBPH face recognizers are good but there are even better ways to perform face recognition like using Histogram of Oriented Gradients (HOGs) and Neural Networks. So the more advanced face recognition algorithms are now a days implemented using a combination of OpenCV and Machine learning. I have plans to write some articles on those more advanced methods as well, so stay tuned!

Download Details:
Author: informramiz
Source Code: https://github.com/informramiz/opencv-face-recognition-python
License: MIT License

#opencv #python #facerecognition

Christa Stehr

1598940617

Install Angular - Angular Environment Setup Process

Angular is a TypeScript based framework that works in synchronization with HTML, CSS, and JavaScript. To work with angular, domain knowledge of these 3 is required.

Installing Node.js and npm
Installing Angular CLI
Creating workspace
Deploying your First App

In this article, you will get to know about the Angular Environment setup process. After reading this article, you will be able to install, setup, create, and launch your own application in Angular. So let’s start!!!

Install Angular in Easy Steps

For Installing Angular on your Machine, there are 2 prerequisites:

Node.js
npm Package Manager

Node.js

First you need to have Node.js installed as Angular require current, active LTS or maintenance LTS version of Node.js

Download and Install Node.js version suitable for your machine’s operating system.

Npm Package Manager

Angular, Angular CLI and Angular applications are dependent on npm packages. By installing Node.js, you have automatically installed the npm Package manager which will be the base for installing angular in your system. To check the presence of npm client and Angular version check of npm client, run this command:

npm -v

Installing Angular CLI

Open Terminal/Command Prompt
To install Angular CLI, run the below command:

npm install -g @angular/cli

· After executing the command, Angular CLI will get installed within some time. You can check it using the following command

ng --version

Workspace Creation

Now as your Angular CLI is installed, you need to create a workspace to work upon your application. Methods for it are:

Using CLI
Using Visual Studio Code

1. Using CLI

To create a workspace:

Navigate to the desired directory where you want to create your workspace using cd command in the Terminal/Command prompt
Then in the directory write this command on your terminal and provide the name of the app which you want to create. In my case I have mentioned DataFlair:

Ng new YourAppName

After running this command, it will prompt you to select from various options about the CSS and other functionalities.

To leave everything to default, simply press the Enter or the Return key.

#angular tutorials #angular cli install #angular environment setup #angular version check #download angular #install angular #install angular cli

Monty Boehm

1659453850

Twitter.jl: Julia Package to Access Twitter API

Twitter.jl

A Julia package for interacting with the Twitter API.

Twitter.jl is a Julia package to work with the Twitter API v1.1. Currently, only the REST API methods are supported; streaming API endpoints aren't implemented at this time.

All functions have required arguments for those parameters required by Twitter and an options keyword argument to provide a Dict{String, String} of optional parameters Twitter API documentation. Most function calls will return either a Dict or an Array <: TwitterType. Bad requests will return the response code from the API (403, 404, etc).

DataFrame methods are defined for functions returning composite types: Tweets, Places, Lists, and Users.

Authentication

Before one can make use of this package, you must create an application on the Twitter's Developer Platform.

Once your application is approved, you can access your dashboard/portal to grab your authentication credentials from the "Details" tab of the application.

Note that you will also want to ensure that your App has Read / Write OAuth access in order to post tweets. You can find out more about this on Stack Overflow.

Installation

To install this package, enter ] on the REPL to bring up Julia's package manager. Then add the package:

julia> ]
(v1.7) pkg> add Twitter

Tip: Press Ctrl+C to return to the julia> prompt.

Usage

To run Twitter.jl, enter the following command in your Julia REPL

julia> using Twitter

Then the a global variable has to be declared with the twitterauth function. This function holds the consumer_key(API Key), consumer_secret(API Key Secret), oauth_token(Access Token), and oauth_secret(Access Token Secret) respectively.

twitterauth("6nOtpXmf...", # API Key
            "sES5Zlj096S...", # API Key Secret
            "98689850-Hj...", # Access Token
            "UroqCVpWKIt...") # Access Token Secret

Ensure you put your credentials in an env file to avoid pushing your secrets to the public 🙀.

Note: This package does not currently support OAuth authentication.

Code examples

See runtests.jl for example function calls.

using Twitter, Test
using JSON, OAuth

# set debugging
ENV["JULIA_DEBUG"]=Twitter

twitterauth(ENV["CONSUMER_KEY"], ENV["CONSUMER_SECRET"], ENV["ACCESS_TOKEN"], ENV["ACCESS_TOKEN_SECRET"])

#get_mentions_timeline
mentions_timeline_default = get_mentions_timeline()
tw = mentions_timeline_default[1]
tw_df = DataFrame(mentions_timeline_default)
@test 0 <= length(mentions_timeline_default) <= 20
@test typeof(mentions_timeline_default) == Vector{Tweets}
@test typeof(tw) == Tweets
@test size(tw_df)[2] == 30

#get_user_timeline
user_timeline_default = get_user_timeline(screen_name = "randyzwitch")
@test typeof(user_timeline_default) == Vector{Tweets}

#get_home_timeline
home_timeline_default = get_home_timeline()
@test typeof(home_timeline_default) == Vector{Tweets}

#get_single_tweet_id
get_tweet_by_id = get_single_tweet_id(id = "434685122671939584")
@test typeof(get_tweet_by_id) == Tweets

#get_search_tweets
duke_tweets = get_search_tweets(q = "#Duke", count = 200)
@test typeof(duke_tweets) <: Dict

#test sending/deleting direct messages
#commenting out because Twitter API changed. Come back to fix
# send_dm = post_direct_messages_send(text = "Testing from Julia, this might disappear later $(time())", screen_name = "randyzwitch")
# get_single_dm = get_direct_messages_show(id = send_dm.id)
# destroy = post_direct_messages_destroy(id = send_dm.id)
# @test typeof(send_dm) == Tweets
# @test typeof(get_single_dm) == Tweets
# @test typeof(destroy) == Tweets

#creating/destroying friendships
add_friend = post_friendships_create(screen_name = "kyrieirving")

unfollow = post_friendships_destroy(screen_name = "kyrieirving")
unfollow_df = DataFrame(unfollow)
@test typeof(add_friend) == Users
@test typeof(unfollow) == Users
@test size(unfollow_df)[2] == 40

# create a cursor for follower ids
follow_cursor_test = get_followers_ids(screen_name = "twitter", count = 10_000)
@test length(follow_cursor_test["ids"]) == 10_000

# create a cursor for friend ids - use barackobama because he follows a lot of accounts!
friend_cursor_test = get_friends_ids(screen_name = "BarackObama", count = 10_000)
@test length(friend_cursor_test["ids"]) == 10_000

# create a test for home timelines
home_t = get_home_timeline(count = 2)
@test length(home_t) > 1

# TEST of cursoring functionality on user timelines
user_t = get_user_timeline(screen_name = "stefanjwojcik", count = 400)
@test length(user_t) == 400
# get the minimum ID of the tweets returned (the earliest)
minid = minimum(x.id for x in user_t);

# now iterate until you hit that tweet: should return 399
# WARNING: current versions of julia cannot use keywords in macros? read here: https://github.com/JuliaLang/julia/pull/29261
# eventually replace since_id = minid
tweets_since = get_user_timeline(screen_name = "stefanjwojcik", count = 400, since_id = 1001808621053898752, include_rts=1)

@test length(tweets_since)>=399

# testing get_mentions_timeline
mentions = get_mentions_timeline(screen_name = "stefanjwojcik", count = 300) 
@test length(mentions) >= 50 #sometimes API doesn't return number requested (twitter API specifies count is the max returned, may be much lower)
@test Tweets<:typeof(mentions[1])

# testing retweets_of_me
my_rts = get_retweets_of_me(count = 300)
@test Tweets<:typeof(my_rts[1])

Want to contribute?

Contributions are welcome! Kindly refer to the contribution guidelines.

Linux:

CodeCov:

Author: Randyzwitch
Source Code: https://github.com/randyzwitch/Twitter.jl
License: View license

#julia #api #twitter