Alfie Mellor

Alfie Mellor

1594096832

Object-Oriented Programming in Python

Tackle the basics of Object-Oriented Programming (OOP) in Python: explore classes, objects, instance methods, attributes and much more!

Object-Oriented programming is a widely used concept to write powerful applications. As a data scientist, you will be required to write applications to process your data, among a range of other things. In this tutorial, you will discover the basics of object-oriented programming in Python. You will learn the following:

  • How to create a class
  • Instantiating objects
  • Adding attributes to a class
  • Defining methods within a class
  • Passing arguments to methods
  • How OOP can be used in Python for finance

OOP: Introduction

Object-oriented programming has some advantages over other design patterns. Development is faster and cheaper, with better software maintainability. This, in turn, leads to higher-quality software, which is also extensible with new methods and attributes. The learning curve is, however, steeper. The concept may be too complex for beginners. Computationally, OOP software is slower, and uses more memory since more lines of code have to be written.

Object-oriented programming is based on the imperative programming paradigm, which uses statements to change a program’s state. It focuses on describing how a program should operate. Examples of imperative programming languages are C, C++, Java, Go, Ruby and Python. This stands in contrast to declarative programming, which focuses on what the computer program should accomplish, without specifying how. Examples are database query languages like SQL and XQuery, where one only tells the computer what data to query from where, but now how to do it.

OOP uses the concept of objects and classes. A class can be thought of as a ‘blueprint’ for objects. These can have their own attributes (characteristics they possess), and methods (actions they perform).

OOP Example

An example of a class is the class Dog. Don’t think of it as a specific dog, or your own dog. We’re describing what a dog is and can do, in general. Dogs usually have a name and age; these are instance attributes. Dogs can also bark; this is a method.

When you talk about a specific dog, you would have an object in programming: an object is an instantiation of a class. This is the basic principle on which object-oriented programming is based. So my dog Ozzy, for example, belongs to the class Dog. His attributes are name = 'Ozzy' and age = '2'. A different dog will have different attributes.

OOP in Python

Python is a great programming language that supports OOP. You will use it to define a class with attributes and methods, which you will then call. Python offers a number of benefits compared to other programming languages like Java, C++ or R. It’s a dynamic language, with high-level data types. This means that development happens much faster than with Java or C++. It does not require the programmer to declare types of variables and arguments. This also makes Python easier to understand and learn for beginners, its code being more readable and intuitive.

How to create a class

To define a class in Python, you can use the class keyword, followed by the class name and a colon. Inside the class, an __init__ method has to be defined with def. This is the initializer that you can later use to instantiate objects. It’s similar to a constructor in Java. __init__ must always be present! It takes one argument: self, which refers to the object itself. Inside the method, the pass keyword is used as of now, because Python expects you to type something there. Remember to use correct indentation!

class Dog:

    def __init__(self):
        pass

Note: self in Python is equivalent to this in C++ or Java.

In this case, you have a (mostly empty) Dog class, but no object yet. Let’s create one!

Instantiating objects

To instantiate an object, type the class name, followed by two brackets. You can assign this to a variable to keep track of the object.

ozzy = Dog()

And print it:

print(ozzy)
<__main__.Dog object at 0x111f47278>

Adding attributes to a class

After printing ozzy, it is clear that this object is a dog. But you haven’t added any attributes yet. Let’s give the Dog class a name and age, by rewriting it:

class Dog:

    def __init__(self, name, age):  
        self.name = name
        self.age = age

You can see that the function now takes two arguments after self: name and age. These then get assigned to self.name and self.age respectively. You can now now create a new ozzy object, with a name and age:

ozzy = Dog("Ozzy", 2)

To access an object’s attributes in Python, you can use the dot notation. This is done by typing the name of the object, followed by a dot and the attribute’s name.

print(ozzy.name)

print(ozzy.age)
Ozzy
2

This can also be combined in a more elaborate sentence:

print(ozzy.name + " is " + str(ozzy.age) + " year(s) old.")
Ozzy is 2 year(s) old.

The str() function is used here to convert the age attribute, which is an integer, to a string, so you can use it in the print() function.

#python #oop #developer

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Object-Oriented Programming in Python
Arvel  Parker

Arvel Parker

1591611780

How to Find Ulimit For user on Linux

How can I find the correct ulimit values for a user account or process on Linux systems?

For proper operation, we must ensure that the correct ulimit values set after installing various software. The Linux system provides means of restricting the number of resources that can be used. Limits set for each Linux user account. However, system limits are applied separately to each process that is running for that user too. For example, if certain thresholds are too low, the system might not be able to server web pages using Nginx/Apache or PHP/Python app. System resource limits viewed or set with the NA command. Let us see how to use the ulimit that provides control over the resources available to the shell and processes.

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MEAN Stack Tutorial MongoDB ExpressJS AngularJS NodeJS

We are going to build a full stack Todo App using the MEAN (MongoDB, ExpressJS, AngularJS and NodeJS). This is the last part of three-post series tutorial.

MEAN Stack tutorial series:

AngularJS tutorial for beginners (Part I)
Creating RESTful APIs with NodeJS and MongoDB Tutorial (Part II)
MEAN Stack Tutorial: MongoDB, ExpressJS, AngularJS and NodeJS (Part III) 👈 you are here
Before completing the app, let’s cover some background about the this stack. If you rather jump to the hands-on part click here to get started.

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Yoshiko  Jones

Yoshiko Jones

1598195340

How to configure AWS SES with Postfix MTA

How do I configure Amazon SES With Postfix mail server to send email under a CentOS/RHEL/Fedora/Ubuntu/Debian Linux server?

Amazon Simple Email Service (SES) is a hosted email service for you to send and receive email using your email addresses and domains. Typically SES used for sending bulk email or routing emails without hosting MTA. We can use Perl/Python/PHP APIs to send an email via SES. Another option is to configure Linux or Unix box running Postfix to route all outgoing emails via SES.

  • » Remove sendmail
  • » Install postfix
  • » Configuring postfix for SES
  • » Test postfix

Procedure to configure AWS SES with Postfix

Before getting started with Amazon SES and Postfix, you need to sign up for AWS, including SES. You need to verify your email address and other settings. Make sure you create a user for SES access and download credentials too.

Step 1 – Uninstall Sendmail if installed

If sendmail installed remove it. Debian/Ubuntu Linux user type the following apt command/apt-get command:

$`` sudo apt --purge remove sendmail

CentOS/RHEL user type the following yum command or dnf command on Fedora/CentOS/RHEL 8.x:

$`` sudo yum remove sendmail

$`` sudo dnf remove sendmail

Sample outputs from CentOS 8 server:

Dependencies resolved.
===============================================================================
 Package           Architecture  Version               Repository         Size
===============================================================================
Removing:
 sendmail          x86_64        8.15.2-32.el8         @AppStream        2.4 M
Removing unused dependencies:
 cyrus-sasl        x86_64        2.1.27-1.el8          @BaseOS           160 k
 procmail          x86_64        3.22-47.el8           @AppStream        369 k

Transaction Summary
===============================================================================
Remove  3 Packages

Freed space: 2.9 M
Is this ok [y/N]: y

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Tyrique  Littel

Tyrique Littel

1597723200

FreeBSD s3cmd failed [SSL CERTIFICATE_VERIFY_FAILED]

When I install s3cmd package on my FreeBSD system and try to use the s3cmd command I get the following error:

_ERROR: Test failed: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (ssl.c:1091)

How do I fix this problem on FreeBSD Unix system?

Amazon Simple Storage Service (s3 ) is object storage through a web service interface or API. You can store all sorts of files. FreeBSD is free and open-source operating systems. s3cmd is a command-line utility for the Unix-like system to upload, download files to AWS S3 service from the command line.

ERROR: Test failed: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed error and solution

This error indicates that you don’t have packages correctly installed, especially SSL certificates. Let us see how to fix this problem and install s3cmd correctly on FreeBSD to get rid of the problem.

How to install s3cmd on FreeBSD

Search for s3cmd package:

$ pkg search s3cmd

Execute the following command and make sure you install Python 3.x package as Python 2 will be removed after 2020:

$ sudo pkg install py37-s3cmd-2.1.0

Updating FreeBSD repository catalogue...
FreeBSD repository is up to date.
All repositories are up to date.
Checking integrity... done (0 conflicting)
The following 8 package(s) will be affected (of 0 checked):

New packages to be INSTALLED:
	libffi: 3.2.1_3
	py37-dateutil: 2.8.1
	py37-magic: 5.38
	py37-s3cmd: 2.1.0
	py37-setuptools: 44.0.0
	py37-six: 1.14.0
	python37: 3.7.8
	readline: 8.0.4

Number of packages to be installed: 8

The process will require 118 MiB more space.

Proceed with this action? [y/N]: y
[rsnapshot] [1/8] Installing readline-8.0.4...
[rsnapshot] [1/8] Extracting readline-8.0.4: 100%
[rsnapshot] [2/8] Installing libffi-3.2.1_3...
....
..
[rsnapshot] [8/8] Extracting py37-s3cmd-2.1.0: 100%
=====
Message from python37-3.7.8:

--
Note that some standard Python modules are provided as separate ports
as they require additional dependencies. They are available as:

py37-gdbm       databases/py-gdbm@py37
py37-sqlite3    databases/py-sqlite3@py37
py37-tkinter    x11-toolkits/py-tkinter@py37

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CentOS Linux 8.2 Released and Here is How to Upgrade it

CentOS Linux 8.2 (2004) released. It is a Linux distribution derived from RHEL (Red Hat Enterprise Linux) 8.2 source code. CentOS was created when Red Hat stopped providing RHEL free. CentOS 8.2 gives complete control of its open-source software packages and is fully customized for research needs or for running a high-performance website without the need for license fees. Let us see what’s new in CentOS 8.2 (2004) and how to upgrade existing CentOS 8.1.1199 server to 8.2.2004 using the command line.

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