Classes in Python

5 Key excerpts on "Classes in Python"

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  eBook - ePub

  An Introduction to Python Programming: A Practical Approach

  step-by-step approach to Python programming with machine learning fundamental and theoretical principles.

  • Dr. Krishna Kumar Mohbey; Dr. Brijesh Bakariya(Author)
  • 2021(Publication Date)
  • BPB Publications

    (Publisher)

  Python, like other general-purpose programming languages, has been an object-oriented language. It enables us to build applications in an object-oriented manner. We can easily develop and use classes and objects in Python. Using classes and objects to construct the software is an object-oriented paradigm. The object is linked to real-world objects such as a computer, a home, a mobile, etc. The OOPS definition emphasizes the development of reusable code. It is a common method of resolving a problem by creating objects. The following are the key concepts of an object-oriented programming paradigm:

  • Class
  • Object
  • Method
  • Data Abstraction and Encapsulation
  • Inheritance
  • Polymorphism

  Introduction to classes

  A set of objects can be described as a class. It's a logical entity with some unique properties and methods. For instance, if you have a student class, it should have an attribute and a method, such as name, age, address, and course.

  Object

  The object is a self-contained entity with state and actions. It could be a laptop, a purse, a phone, a table, a pencil, or something else. In Python, everything is an object, with attributes and methods on almost everything. A class must construct an object to assign memory when it is defined.

  Method

  In Python, a method is like a function, except that it is linked to objects and classes. Except for two big variations, Python methods and functions are similar.

  • For the object for which it is named, the method is used implicitly.
  • Data in the class is accessible to the method.

  Data abstraction and encapsulation

  In object-oriented programming, encapsulation is also essential. It's used to limit access to variables and methods. Encapsulation protects code and data from accidental modification by wrapping them together in a single device.

  Abstraction is a technique for hiding internal information and displaying only the functionalities. The term abstract

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  eBook - ePub

  Designing Microservices using Django

  Structuring, Deploying and Managing the Microservices Architecture with Django

  • Shayank Jain(Author)
  • 2020(Publication Date)
  • BPB Publications

    (Publisher)

  HAPTER 2

  Major Pillars of OOPS with Python

  P ython is an object-oriented programming (OOP ) language. It also supports many features of OOPS. This chapter covers all OOP concepts, which are available in Python. We included this chapter in the book, because OOP is a very important part of every object-oriented language. In this chapter, we have tried to explain the OOP concept with the simplest terms and real-world examples.

  Structure

  • Introduction to object-oriented programming (OOP) language
  • Basic idea of object
  • What is class?
  • Decorators in Python
  • Introduction of class method and static method in Python
  • Inheritance
    • Single inheritance
    • Multiple inheritance
    • Multilevel inheritance
  • Encapsulation
  • Polymorphism
  • Method overloading
  • Method overriding
  • Abstraction

  Objective

  At the end of this chapter, you should easily understand the object, classes, class variables, static method, class methods, major pillars of OOPs, and decorators.

  Introduction to object-oriented programming (OOP) language

  Earlier, while writing code programmers used to face the following difficulties:

  • Code duplication
  • less security of the code
  • code following the procedural programming
  • Difficulty to manage long codes
  • less readability of code due to lack of relevance to the real world

  To resolve these issues, OOP concepts were driven. At first, OOP was introduced with the C++ language. After the success of OOP, most of the programming languages include this functionality. Mentioned below are the main features of the OOPs concept or we can also call them the major pillars of Python:

  • Object
  • Class
  • Inheritance
  • Encapsulation
  • Polymorphism
  • Abstraction

  Basic idea of object

  This is the very common definition of object, which is available on the internet: The object is a real-world entity, which has attributes and behavior. For example, a car is an object which has attributes such as color, brand, tiers, seats, speed, and more.

  What is class?

  It is the collection of objects, functions, and statements. We can also say that it is a user-defined structure, which has collective data related to the class. For example, we have class Engineering_college

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  eBook - ePub

  Scripting with Objects

  A Comparative Presentation of Object-Oriented Scripting with Perl and Python

  • Avinash C. Kak(Author)
  • 2017(Publication Date)
  • Wiley

    (Publisher)

  7

  The Notion of a Class in Python

  Since the previous chapter has already introduced the rudiments of the OO vocabulary, in this chapter we can proceed directly to show how the various object-oriented notions at the level of a class are implemented in Python. For a reader skipping through the book, he/she may wish to first review the introductory material in Chapter 6 before proceeding further.

  We want to begin this chapter by reminding the reader about the distinction between objects in general, on the one hand, and classes and instances, on the other. This distinction is particularly important in this chapter because practically all entities in Python are objects in the sense of possessing either retrievable data attributes or invocable methods or both using the dot operator that is commonly used in object-oriented programming for such purposes. A user-defined class (for that matter, any class) in Python is an object with certain system-supplied attributes. These are not to be confused with the more traditional programmer-supplied attributes such as the class variables and the instance variables, and the programmer-supplied methods. By the same token, an instance constructed from a class is an object with certain other system-supplied attributes that again are not to be confused with the programmer-supplied instance variables associated with an instance and the programmer-supplied methods that can be invoked on an instance.

  With regard to the OO terminology commonly used in Python, when referring to the data attributes of a class, we will continue to use instance variables and class variables in the same sense as before. Instance variables of a class will represent the properties of the instances constructed from a class; in general, these would be different for different instances. On the other hand, class variables will represent properties that are global for all the instances constructed from a class. Both the instance variables and class variables are examples of the attributes of a class. However, we will now use the word attribute

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  eBook - ePub

  Python Fundamentals

  A practical guide for learning Python, complete with real-world projects for you to explore

  • Ryan Marvin, Mark Ng'ang'a, Amos Omondi(Authors)
  • 2018(Publication Date)
  • Packt Publishing

    (Publisher)

  For example, when building a house, you'd follow a blueprint that tells you things such as how many rooms the house has, where the rooms are positioned relative to one another, or how the plumbing and electrical circuitry is laid out. In OOP, this building blueprint would be the class, while the house would be the instance/object.

  In the earlier lessons, we mentioned that everything in Python is an object. Every data type and data structure you've encountered thus far, from lists and strings to integers, functions, and others, are objects. This is why when we run the type function on any object, it will have the following output:

  >>> type([1, 2, 3]) <class 'list'> >>> type("foobar") <class 'str'> >>> type({"a": 1, "b": 2}) <class 'dict'> >>> def func(): return True ... >>> type(func) <class 'function'> >>>

  You'll note that calling the type function on each object prints out that it is an instance of a specific class. Lists are instances of the list class, strings are instances of the str class, dictionaries are instances of the dict class, and so on and so forth.

  Each class is a blueprint that defines what behaviors and attributes objects will contain and how they'll behave; for example, all of the lists that you create will have the lists.append() method, which allows you to add elements to the list.

  Here, we are creating an instance of the list class and printing out the append and remove methods. It tells us that they are methods of the list object we've instantiated:

  >>> l = [1, 2, 3, 4, 5] # create a list object >>> print(l.append) <built-in method append of list object at 0x10dd36a08> >>> print(l.remove) <built-in method remove of list object at 0x10dd36a08> >>>

  Note

  In this chapter, we will use the terms instance and object synonymously.

  Defining a Class in Python

  In our example, we'll be creating the blueprint for a person. Compared to most languages, the syntax for defining a simple class is very minimal in Python.

  Exercise 31: Creating a Class

  In this exercise, we will create our first class, called Person . The steps are as follows:

  1. Declare the class using the Python keyword class , followed by the class name Person . In the block, we have the Python keyword pass , which is used as a placeholder for where the rest of our class definition will go:>>> class Person: ... pass ... >>>

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  eBook - ePub

  Python for Professionals

  Learning Python as a Second Language

  • Matt Telles(Author)
  • 2019(Publication Date)
  • BPB Publications

    (Publisher)

  This shows you that the interpreter will not allow you to retrieve that variable. This is somewhat equivalent to the C++ or Java private access declaration, but not exactly. As we will see when we talk about inheritance, derived classes do not inherit access to these private variables.

  The example above, however, does illustrate some of the ways in which Python helps you to do the OOP concept of abstraction. By binding the data (in this case, the internal variable) together with the methods (the get and set methods of the class) we abstract away the user from worrying about how the underlying data structure is built. Python takes the idea of abstraction and trusts the end developer a bit to worry about how it is done. They don’t have to ignore that they can see the data structure within the class they are using but it is the Pythonic way to do so. Trust those that went before you.

  Inheritance

  Inheritance is the process of creating a new class from the basics of an existing class. Like genetics, the new class inherits all of its innate abilities from its parent but also adds its own unique abilities and attributes.

  Python classes may be slightly different from the ones you’ve used in other languages but the basic concepts are there. You create an instance of a class using the name of the class as if it were a function that generated an object. For our InternalTest class above, we created an instance of it by using:

  it = InternalTest(4)

  As you see, there is a constructor, alas Java or C++, called __init__ . There is a destructor __del__ as well, although it is not usually implemented for the majority of Python code. Memory management is all done by the Python interpreter, freeing the developer to worry more about the implementation of features and less about the underlying OS. This also makes Python more flexible and portable.

  Most OOP languages have some sort of inheritance methodology. Basically, you can create a class that is based upon another class, which inherits

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