Recoil.js & simple global state

In its simplest implementation, Recoil allows you to hold global state in your React App, and then use or update it from any component.

Recoil shines because of how simple it is to use and how little code it takes to get up and running. Recoil eliminates long paths of passed props, and unlike other global state libraries like Redux, there is very little learning curve or boilerplate code for setup.

Today we are going to build an app that demonstrates how simple Recoil is to set up and use.

This guide assumes that you have Node ≥8.10 and NPM ≥ 5.6 on your machine and that you are comfortable using React. Experience with React Hooks will make this even easier.

---

Basic Recoil Functions and hooks:

There are a few functions and hooks that we should get familiar with before building our sample app. Atom, useRecoilState(), useRecoilValue(), and selector.

Atom

An atom represents a single piece of state that can be read or written to from any component. Anytime an atom is updated, all of the components subscribed to it will update. When you create an atom, give it a unique key (unique across all atoms and selectors), and a default value (usually an empty string or object).

const dataAtom = atom({
   key: 'dataAtom',
   default: '',
});

useRecoilState()

Import and use this hook when you need to read AND write to an atom. Pass your atom touseRecoilState(). In our restructuring assignment, we are going to assign one variable for calling our state, and one for updating it.

#javascript #web-development #recoiljs #react #programming

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Buddha Community

NBB: Ad-hoc CLJS Scripting on Node.js

Nbb

Not babashka. Node.js babashka!?

Ad-hoc CLJS scripting on Node.js.

Status

Experimental. Please report issues here.

Goals and features

Nbb's main goal is to make it easy to get started with ad hoc CLJS scripting on Node.js.

Additional goals and features are:

• Fast startup without relying on a custom version of Node.js.
• Small artifact (current size is around 1.2MB).
• First class macros.
• Support building small TUI apps using Reagent.
• Complement babashka with libraries from the Node.js ecosystem.

Requirements

Nbb requires Node.js v12 or newer.

How does this tool work?

CLJS code is evaluated through SCI, the same interpreter that powers babashka. Because SCI works with advanced compilation, the bundle size, especially when combined with other dependencies, is smaller than what you get with self-hosted CLJS. That makes startup faster. The trade-off is that execution is less performant and that only a subset of CLJS is available (e.g. no deftype, yet).

Usage

Install nbb from NPM:

$ npm install nbb -g

Omit -g for a local install.

Try out an expression:

$ nbb -e '(+ 1 2 3)'
6

And then install some other NPM libraries to use in the script. E.g.:

$ npm install csv-parse shelljs zx

Create a script which uses the NPM libraries:

(ns script
  (:require ["csv-parse/lib/sync$default" :as csv-parse]
            ["fs" :as fs]
            ["path" :as path]
            ["shelljs$default" :as sh]
            ["term-size$default" :as term-size]
            ["zx$default" :as zx]
            ["zx$fs" :as zxfs]
            [nbb.core :refer [*file*]]))

(prn (path/resolve "."))

(prn (term-size))

(println (count (str (fs/readFileSync *file*))))

(prn (sh/ls "."))

(prn (csv-parse "foo,bar"))

(prn (zxfs/existsSync *file*))

(zx/$ #js ["ls"])

Call the script:

$ nbb script.cljs
"/private/tmp/test-script"
#js {:columns 216, :rows 47}
510
#js ["node_modules" "package-lock.json" "package.json" "script.cljs"]
#js [#js ["foo" "bar"]]
true
$ ls
node_modules
package-lock.json
package.json
script.cljs

Macros

Nbb has first class support for macros: you can define them right inside your .cljs file, like you are used to from JVM Clojure. Consider the plet macro to make working with promises more palatable:

(defmacro plet
  [bindings & body]
  (let [binding-pairs (reverse (partition 2 bindings))
        body (cons 'do body)]
    (reduce (fn [body [sym expr]]
              (let [expr (list '.resolve 'js/Promise expr)]
                (list '.then expr (list 'clojure.core/fn (vector sym)
                                        body))))
            body
            binding-pairs)))

Using this macro we can look async code more like sync code. Consider this puppeteer example:

(-> (.launch puppeteer)
      (.then (fn [browser]
               (-> (.newPage browser)
                   (.then (fn [page]
                            (-> (.goto page "https://clojure.org")
                                (.then #(.screenshot page #js{:path "screenshot.png"}))
                                (.catch #(js/console.log %))
                                (.then #(.close browser)))))))))

Using plet this becomes:

(plet [browser (.launch puppeteer)
       page (.newPage browser)
       _ (.goto page "https://clojure.org")
       _ (-> (.screenshot page #js{:path "screenshot.png"})
             (.catch #(js/console.log %)))]
      (.close browser))

See the puppeteer example for the full code.

Since v0.0.36, nbb includes promesa which is a library to deal with promises. The above plet macro is similar to promesa.core/let.

Startup time

$ time nbb -e '(+ 1 2 3)'
6
nbb -e '(+ 1 2 3)'   0.17s  user 0.02s system 109% cpu 0.168 total

The baseline startup time for a script is about 170ms seconds on my laptop. When invoked via npx this adds another 300ms or so, so for faster startup, either use a globally installed nbb or use $(npm bin)/nbb script.cljs to bypass npx.

Dependencies

NPM dependencies

Nbb does not depend on any NPM dependencies. All NPM libraries loaded by a script are resolved relative to that script. When using the Reagent module, React is resolved in the same way as any other NPM library.

Classpath

To load .cljs files from local paths or dependencies, you can use the --classpath argument. The current dir is added to the classpath automatically. So if there is a file foo/bar.cljs relative to your current dir, then you can load it via (:require [foo.bar :as fb]). Note that nbb uses the same naming conventions for namespaces and directories as other Clojure tools: foo-bar in the namespace name becomes foo_bar in the directory name.

To load dependencies from the Clojure ecosystem, you can use the Clojure CLI or babashka to download them and produce a classpath:

$ classpath="$(clojure -A:nbb -Spath -Sdeps '{:aliases {:nbb {:replace-deps {com.github.seancorfield/honeysql {:git/tag "v2.0.0-rc5" :git/sha "01c3a55"}}}}}')"

and then feed it to the --classpath argument:

$ nbb --classpath "$classpath" -e "(require '[honey.sql :as sql]) (sql/format {:select :foo :from :bar :where [:= :baz 2]})"
["SELECT foo FROM bar WHERE baz = ?" 2]

Currently nbb only reads from directories, not jar files, so you are encouraged to use git libs. Support for .jar files will be added later.

Current file

The name of the file that is currently being executed is available via nbb.core/*file* or on the metadata of vars:

(ns foo
  (:require [nbb.core :refer [*file*]]))

(prn *file*) ;; "/private/tmp/foo.cljs"

(defn f [])
(prn (:file (meta #'f))) ;; "/private/tmp/foo.cljs"

Reagent

Nbb includes reagent.core which will be lazily loaded when required. You can use this together with ink to create a TUI application:

$ npm install ink

ink-demo.cljs:

(ns ink-demo
  (:require ["ink" :refer [render Text]]
            [reagent.core :as r]))

(defonce state (r/atom 0))

(doseq [n (range 1 11)]
  (js/setTimeout #(swap! state inc) (* n 500)))

(defn hello []
  [:> Text {:color "green"} "Hello, world! " @state])

(render (r/as-element [hello]))

Promesa

Working with callbacks and promises can become tedious. Since nbb v0.0.36 the promesa.core namespace is included with the let and do! macros. An example:

(ns prom
  (:require [promesa.core :as p]))

(defn sleep [ms]
  (js/Promise.
   (fn [resolve _]
     (js/setTimeout resolve ms))))

(defn do-stuff
  []
  (p/do!
   (println "Doing stuff which takes a while")
   (sleep 1000)
   1))

(p/let [a (do-stuff)
        b (inc a)
        c (do-stuff)
        d (+ b c)]
  (prn d))

$ nbb prom.cljs
Doing stuff which takes a while
Doing stuff which takes a while
3

Also see API docs.

Js-interop

Since nbb v0.0.75 applied-science/js-interop is available:

(ns example
  (:require [applied-science.js-interop :as j]))

(def o (j/lit {:a 1 :b 2 :c {:d 1}}))

(prn (j/select-keys o [:a :b])) ;; #js {:a 1, :b 2}
(prn (j/get-in o [:c :d])) ;; 1

Most of this library is supported in nbb, except the following:

• destructuring using :syms
• property access using .-x notation. In nbb, you must use keywords.

See the example of what is currently supported.

Examples

See the examples directory for small examples.

Also check out these projects built with nbb:

• c64core: retrocompute aesthetics twitter bot
• gallery.cljs: script to download walpapers from windowsonearth.org.
• nbb-action-example: example of a Github action built with nbb.

API

See API documentation.

Migrating to shadow-cljs

See this gist on how to convert an nbb script or project to shadow-cljs.

Build

Prequisites:

• babashka >= 0.4.0
• Clojure CLI >= 1.10.3.933
• Node.js 16.5.0 (lower version may work, but this is the one I used to build)

To build:

• Clone and cd into this repo
• bb release

Run bb tasks for more project-related tasks.

Download Details:
Author: borkdude
Download Link: Download The Source Code
Official Website: https://github.com/borkdude/nbb 
License: EPL-1.0

#node #javascript

Hire Dedicated Node.js Developers - Hire Node.js Developers

If you look at the backend technology used by today’s most popular apps there is one thing you would find common among them and that is the use of NodeJS Framework. Yes, the NodeJS framework is that effective and successful.

If you wish to have a strong backend for efficient app performance then have NodeJS at the backend.

WebClues Infotech offers different levels of experienced and expert professionals for your app development needs. So hire a dedicated NodeJS developer from WebClues Infotech with your experience requirement and expertise.

So what are you waiting for? Get your app developed with strong performance parameters from WebClues Infotech

For inquiry click here: https://www.webcluesinfotech.com/hire-nodejs-developer/

Book Free Interview: https://bit.ly/3dDShFg

#hire dedicated node.js developers #hire node.js developers #hire top dedicated node.js developers #hire node.js developers in usa & india #hire node js development company #hire the best node.js developers & programmers

Why use Node.js for Web Development? Benefits and Examples of Apps

Front-end web development has been overwhelmed by JavaScript highlights for quite a long time. Google, Facebook, Wikipedia, and most of all online pages use JS for customer side activities. As of late, it additionally made a shift to cross-platform mobile development as a main technology in React Native, Nativescript, Apache Cordova, and other crossover devices. 

Throughout the most recent couple of years, Node.js moved to backend development as well. Designers need to utilize a similar tech stack for the whole web project without learning another language for server-side development. Node.js is a device that adjusts JS usefulness and syntax to the backend. 

What is Node.js? 

Node.js isn’t a language, or library, or system. It’s a runtime situation: commonly JavaScript needs a program to work, however Node.js makes appropriate settings for JS to run outside of the program. It’s based on a JavaScript V8 motor that can run in Chrome, different programs, or independently. 

The extent of V8 is to change JS program situated code into machine code — so JS turns into a broadly useful language and can be perceived by servers. This is one of the advantages of utilizing Node.js in web application development: it expands the usefulness of JavaScript, permitting designers to coordinate the language with APIs, different languages, and outside libraries.

What Are the Advantages of Node.js Web Application Development? 

Of late, organizations have been effectively changing from their backend tech stacks to Node.js. LinkedIn picked Node.js over Ruby on Rails since it took care of expanding responsibility better and decreased the quantity of servers by multiple times. PayPal and Netflix did something comparative, just they had a goal to change their design to microservices. We should investigate the motivations to pick Node.JS for web application development and when we are planning to hire node js developers. 

Amazing Tech Stack for Web Development 

The principal thing that makes Node.js a go-to environment for web development is its JavaScript legacy. It’s the most well known language right now with a great many free devices and a functioning local area. Node.js, because of its association with JS, immediately rose in ubiquity — presently it has in excess of 368 million downloads and a great many free tools in the bundle module. 

Alongside prevalence, Node.js additionally acquired the fundamental JS benefits: 

• quick execution and information preparing; 
• exceptionally reusable code; 
• the code is not difficult to learn, compose, read, and keep up; 
• tremendous asset library, a huge number of free aides, and a functioning local area. 

In addition, it’s a piece of a well known MEAN tech stack (the blend of MongoDB, Express.js, Angular, and Node.js — four tools that handle all vital parts of web application development). 

Designers Can Utilize JavaScript for the Whole Undertaking 

This is perhaps the most clear advantage of Node.js web application development. JavaScript is an unquestionable requirement for web development. Regardless of whether you construct a multi-page or single-page application, you need to know JS well. On the off chance that you are now OK with JavaScript, learning Node.js won’t be an issue. Grammar, fundamental usefulness, primary standards — every one of these things are comparable. 

In the event that you have JS designers in your group, it will be simpler for them to learn JS-based Node than a totally new dialect. What’s more, the front-end and back-end codebase will be basically the same, simple to peruse, and keep up — in light of the fact that they are both JS-based. 

A Quick Environment for Microservice Development 

There’s another motivation behind why Node.js got famous so rapidly. The environment suits well the idea of microservice development (spilling stone monument usefulness into handfuls or many more modest administrations). 

Microservices need to speak with one another rapidly — and Node.js is probably the quickest device in information handling. Among the fundamental Node.js benefits for programming development are its non-obstructing algorithms.

Node.js measures a few demands all at once without trusting that the first will be concluded. Many microservices can send messages to one another, and they will be gotten and addressed all the while. 

Versatile Web Application Development 

Node.js was worked in view of adaptability — its name really says it. The environment permits numerous hubs to run all the while and speak with one another. Here’s the reason Node.js adaptability is better than other web backend development arrangements. 

Node.js has a module that is liable for load adjusting for each running CPU center. This is one of numerous Node.js module benefits: you can run various hubs all at once, and the environment will naturally adjust the responsibility. 

Node.js permits even apportioning: you can part your application into various situations. You show various forms of the application to different clients, in light of their age, interests, area, language, and so on. This builds personalization and diminishes responsibility. Hub accomplishes this with kid measures — tasks that rapidly speak with one another and share a similar root. 

What’s more, Node’s non-hindering solicitation handling framework adds to fast, letting applications measure a great many solicitations. 

Control Stream Highlights

Numerous designers consider nonconcurrent to be one of the two impediments and benefits of Node.js web application development. In Node, at whatever point the capacity is executed, the code consequently sends a callback. As the quantity of capacities develops, so does the number of callbacks — and you end up in a circumstance known as the callback damnation. 

In any case, Node.js offers an exit plan. You can utilize systems that will plan capacities and sort through callbacks. Systems will associate comparable capacities consequently — so you can track down an essential component via search or in an envelope. At that point, there’s no compelling reason to look through callbacks.

 

Final Words

So, these are some of the top benefits of Nodejs in web application development. This is how Nodejs is contributing a lot to the field of web application development. 

I hope now you are totally aware of the whole process of how Nodejs is really important for your web project. If you are looking to hire a node js development company in India then I would suggest that you take a little consultancy too whenever you call. 

Good Luck!

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Why is Vue JS the most Preferred Choice for Responsive Web Application Development?

For more than two decades, JavaScript has facilitated businesses to develop responsive web applications for their customers. Used both client and server-side, JavaScript enables you to bring dynamics to pages through expanded functionality and real-time modifications.

Did you know!

According to a web development survey 2020, JavaScript is the most used language for the 8th year, with 67.7% of people choosing it. With this came up several javascript frameworks for frontend, backend development, or even testing.

And one such framework is Vue.Js. It is used to build simple projects and can also be advanced to create sophisticated apps using state-of-the-art tools. Beyond that, some other solid reasons give Vuejs a thumbs up for responsive web application development.

Want to know them? Then follow this blog until the end. Through this article, I will describe all the reasons and benefits of Vue js development. So, stay tuned.

Vue.Js - A Brief Introduction

Released in the year 2014 for public use, Vue.Js is an open-source JavaScript framework used to create UIs and single-page applications. It has over 77.4 million likes on Github for creating intuitive web interfaces.

The recent version is Vue.js 2.6, and is the second most preferred framework according to Stack Overflow Developer Survey 2019.

Every Vue.js development company is widely using the framework across the world for responsive web application development. It is centered around the view layer, provides a lot of functionality for the view layer, and builds single-page web applications.

Some most astonishing stats about Vue.Js:

• Vue was ranked #2 in the Front End JavaScript Framework rankings in the State of JS 2019 survey by developers.

• Approximately 427k to 693k sites are built with Vue js, according to Wappalyzer and BuiltWith statistics of June 2020.

• According to the State of JS 2019 survey, 40.5% of JavaScript developers are currently using Vue, while 34.5% have shown keen interest in using it in the future.

• In Stack Overflow's Developer Survey 2020, Vue was ranked the 3rd most popular front-end JavaScript framework.

Why is Vue.Js so popular?

• High-speed run-time performance
• Vue.Js uses a virtual DOM.
• The main focus is on the core library, while the collaborating libraries handle other features such as global state management and routing.
• Vue.JS provides responsive visual components.

Top 7 Reasons to Choose Vue JS for Web Application Development

Vue js development has certain benefits, which will encourage you to use it in your projects. For example, Vue.js is similar to Angular and React in many aspects, and it continues to enjoy increasing popularity compared to other frameworks.

The framework is only 20 kilobytes in size, making it easy for you to download files instantly. Vue.js easily beats other frameworks when it comes to loading times and usage.

Take a look at the compelling advantages of using Vue.Js for web app development.

#1 Simple Integration

Vue.Js is popular because it allows you to integrate Vue.js into other frameworks such as React, enabling you to customize the project as per your needs and requirements.

It helps you build apps with Vue.js from scratch and introduce Vue.js elements into their existing apps. Due to its ease of integration, Vue.js is becoming a popular choice for web development as it can be used with various existing web applications.

You can feel free to include Vue.js CDN and start using it. Most third-party Vue components and libraries are additionally accessible and supported with the Vue.js CDN.

You don't need to set up node and npm to start using Vue.js. This implies that it helps develop new web applications, just like modifying previous applications.

The diversity of components allows you to create different types of web applications and replace existing frameworks. In addition, you can also choose to hire Vue js developers to use the technology to experiment with many other JavaScript applications.

#2 Easy to Understand

One of the main reasons for the growing popularity of Vue.Js is that the framework is straightforward to understand for individuals. This means that you can easily add Vue.Js to your web projects.

Also, Vue.Js has a well-defined architecture for storing your data with life-cycle and custom methods. Vue.Js also provides additional features such as watchers, directives, and computed properties, making it extremely easy to build modern apps and web applications with ease.

Another significant advantage of using the Vue.Js framework is that it makes it easy to build small and large-scale web applications in the shortest amount of time.

#3 Well-defined Ecosystem

The VueJS ecosystem is vibrant and well-defined, allowing Vue.Js development company to switch users to VueJS over other frameworks for web app development.

Without spending hours, you can easily find solutions to your problems. Furthermore, VueJs lets you choose only the building blocks you need.

Although the main focus of Vue is the view layer, with the help of Vue Router, Vue Test Utils, Vuex, and Vue CLI, you can find solutions and recommendations for frequently occurring problems.

The problems fall into these categories, and hence it becomes easy for programmers to get started with coding right away and not waste time figuring out how to use these tools.

The Vue ecosystem is easy to customize and scales between a library and a framework. Compared to other frameworks, its development speed is excellent, and it can also integrate different projects. This is the reason why most website development companies also prefer the Vue.Js ecosystem over others.

#4 Flexibility

Another benefit of going with Vue.Js for web app development needs is flexibility. Vue.Js provides an excellent level of flexibility. And makes it easier for web app development companies to write their templates in HTML, JavaScript, or pure JavaScript using virtual nodes.

Another significant benefit of using Vue.Js is that it makes it easier for developers to work with tools like templating engines, CSS preprocessors, and type checking tools like TypeScript.

#5 Two-Way Communication

Vue.Js is an excellent option for you because it encourages two-way communication. This has become possible with the MVVM architecture to handle HTML blocks. In this way, Vue.Js is very similar to Angular.Js, making it easier to handle HTML blocks as well.

With Vue.Js, two-way data binding is straightforward. This means that any changes made by the developer to the UI are passed to the data, and the changes made to the data are reflected in the UI.

This is also one reason why Vue.Js is also known as reactive because it can react to changes made to the data. This sets it apart from other libraries such as React.Js, which are designed to support only one-way communication.

#6 Detailed Documentation

One essential thing is well-defined documentation that helps you understand the required mechanism and build your application with ease. It shows all the options offered by the framework and related best practice examples.

Vue has excellent docs, and its API references are one of the best in the industry. They are well written, clear, and accessible in dealing with everything you need to know to build a Vue application.

Besides, the documentation at Vue.js is constantly improved and updated. It also includes a simple introductory guide and an excellent overview of the API. Perhaps, this is one of the most detailed documentation available for this type of language.

#7 Large Community Support

Support for the platform is impressive. In 2018, support continued to impress as every question was answered diligently. Over 6,200 problems were solved with an average resolution time of just six hours.

To support the community, there are frequent release cycles of updated information. Furthermore, the community continues to grow and develop with backend support from developers.

Wrapping Up

VueJS is an incredible choice for responsive web app development. Since it is lightweight and user-friendly, it builds a fast and integrated web application. The capabilities and potential of VueJS for web app development are extensive.

While Vuejs is simple to get started with, using it to build scalable web apps requires professionalism. Hence, you can approach a top Vue js development company in India to develop high-performing web apps.

Equipped with all the above features, it doesn't matter whether you want to build a small concept app or a full-fledged web app; Vue.Js is the most performant you can rely on.

Original source

 

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Python Global Variables – How to Define a Global Variable Example

In this article, you will learn the basics of global variables.

To begin with, you will learn how to declare variables in Python and what the term 'variable scope' actually means.

Then, you will learn the differences between local and global variables and understand how to define global variables and how to use the global keyword.

What Are Variables in Python and How Do You Create Them? An Introduction for Beginners

You can think of variables as storage containers.

They are storage containers for holding data, information, and values that you would like to save in the computer's memory. You can then reference or even manipulate them at some point throughout the life of the program.

A variable has a symbolic name, and you can think of that name as the label on the storage container that acts as its identifier.

The variable name will be a reference and pointer to the data stored inside it. So, there is no need to remember the details of your data and information – you only need to reference the variable name that holds that data and information.

When giving a variable a name, make sure that it is descriptive of the data it holds. Variable names need to be clear and easily understandable both for your future self and the other developers you may be working with.

Now, let's see how to actually create a variable in Python.

When declaring variables in Python, you don't need to specify their data type.

For example, in the C programming language, you have to mention explicitly the type of data the variable will hold.

So, if you wanted to store your age which is an integer, or int type, this is what you would have to do in C:

#include <stdio.h>
 
int main(void)
{
  int age = 28;
  // 'int' is the data type
  // 'age' is the name 
  // 'age' is capable of holding integer values
  // positive/negative whole numbers or 0
  // '=' is the assignment operator
  // '28' is the value
}

However, this is how you would write the above in Python:

age = 28

#'age' is the variable name, or identifier
# '=' is the assignment operator
#'28' is the value assigned to the variable, so '28' is the value of 'age'

The variable name is always on the left-hand side, and the value you want to assign goes on the right-hand side after the assignment operator.

Keep in mind that you can change the values of variables throughout the life of a program:

my_age = 28

print(f"My age in 2022 is {my_age}.")

my_age = 29

print(f"My age in 2023 will be {my_age}.")

#output

#My age in 2022 is 28.
#My age in 2023 will be 29.

You keep the same variable name, my_age, but only change the value from 28 to 29.

What Does Variable Scope in Python Mean?

Variable scope refers to the parts and boundaries of a Python program where a variable is available, accessible, and visible.

There are four types of scope for Python variables, which are also known as the LEGB rule:

• Local,
• Enclosing,
• Global,
• Built-in.

For the rest of this article, you will focus on learning about creating variables with global scope, and you will understand the difference between the local and global variable scopes.

How to Create Variables With Local Scope in Python

Variables defined inside a function's body have local scope, which means they are accessible only within that particular function. In other words, they are 'local' to that function.

You can only access a local variable by calling the function.

def learn_to_code():
    #create local variable
    coding_website = "freeCodeCamp"
    print(f"The best place to learn to code is with {coding_website}!")

#call function
learn_to_code()


#output

#The best place to learn to code is with freeCodeCamp!

Look at what happens when I try to access that variable with a local scope from outside the function's body:

def learn_to_code():
    #create local variable
    coding_website = "freeCodeCamp"
    print(f"The best place to learn to code is with {coding_website}!")

#try to print local variable 'coding_website' from outside the function
print(coding_website)

#output

#NameError: name 'coding_website' is not defined

It raises a NameError because it is not 'visible' in the rest of the program. It is only 'visible' within the function where it was defined.

How to Create Variables With Global Scope in Python

When you define a variable outside a function, like at the top of the file, it has a global scope and it is known as a global variable.

A global variable is accessed from anywhere in the program.

You can use it inside a function's body, as well as access it from outside a function:

#create a global variable
coding_website = "freeCodeCamp"

def learn_to_code():
    #access the variable 'coding_website' inside the function
    print(f"The best place to learn to code is with {coding_website}!")

#call the function
learn_to_code()

#access the variable 'coding_website' from outside the function
print(coding_website)

#output

#The best place to learn to code is with freeCodeCamp!
#freeCodeCamp

What happens when there is a global and local variable, and they both have the same name?

#global variable
city = "Athens"

def travel_plans():
    #local variable with the same name as the global variable
    city = "London"
    print(f"I want to visit {city} next year!")

#call function - this will output the value of local variable
travel_plans()

#reference global variable - this will output the value of global variable
print(f"I want to visit {city} next year!")

#output

#I want to visit London next year!
#I want to visit Athens next year!

In the example above, maybe you were not expecting that specific output.

Maybe you thought that the value of city would change when I assigned it a different value inside the function.

Maybe you expected that when I referenced the global variable with the line print(f" I want to visit {city} next year!"), the output would be #I want to visit London next year! instead of #I want to visit Athens next year!.

However, when the function was called, it printed the value of the local variable.

Then, when I referenced the global variable outside the function, the value assigned to the global variable was printed.

They didn't interfere with one another.

That said, using the same variable name for global and local variables is not considered a best practice. Make sure that your variables don't have the same name, as you may get some confusing results when you run your program.

How to Use the global Keyword in Python

What if you have a global variable but want to change its value inside a function?

Look at what happens when I try to do that:

#global variable
city = "Athens"

def travel_plans():
    #First, this is like when I tried to access the global variable defined outside the function. 
    # This works fine on its own, as you saw earlier on.
    print(f"I want to visit {city} next year!")

    #However, when I then try to re-assign a different value to the global variable 'city' from inside the function,
    #after trying to print it,
    #it will throw an error
    city = "London"
    print(f"I want to visit {city} next year!")

#call function
travel_plans()

#output

#UnboundLocalError: local variable 'city' referenced before assignment

By default Python thinks you want to use a local variable inside a function.

So, when I first try to print the value of the variable and then re-assign a value to the variable I am trying to access, Python gets confused.

The way to change the value of a global variable inside a function is by using the global keyword:

#global variable
city = "Athens"

#print value of global variable
print(f"I want to visit {city} next year!")

def travel_plans():
    global city
    #print initial value of global variable
    print(f"I want to visit {city} next year!")
    #assign a different value to global variable from within function
    city = "London"
    #print new value
    print(f"I want to visit {city} next year!")

#call function
travel_plans()

#print value of global variable
print(f"I want to visit {city} next year!")

Use the global keyword before referencing it in the function, as you will get the following error: SyntaxError: name 'city' is used prior to global declaration.

Earlier, you saw that you couldn't access variables created inside functions since they have local scope.

The global keyword changes the visibility of variables declared inside functions.

def learn_to_code():
   global coding_website
   coding_website = "freeCodeCamp"
   print(f"The best place to learn to code is with {coding_website}!")

#call function
learn_to_code()

#access variable from within the function
print(coding_website)

#output

#The best place to learn to code is with freeCodeCamp!
#freeCodeCamp

Conclusion

And there you have it! You now know the basics of global variables in Python and can tell the differences between local and global variables.

I hope you found this article useful.

You'll start from the basics and learn in an interactive and beginner-friendly way. You'll also build five projects at the end to put into practice and help reinforce what you've learned.

Thanks for reading and happy coding!

Source: https://www.freecodecamp.org/news/python-global-variables-examples/

#python