Classes & Objects in Python

  • Class − A user-defined prototype for an object that defines a set of attributes that characterize any object of the class. The attributes are data members (class variables and instance variables) and methods, accessed via dot notation.
  • Object − A unique instance of a data structure that’s defined by its class. An object comprises both data members (class variables and instance variables) and methods.

A First Look at Classes :

The simplest form of class definition looks like this:

class ClassName:
<statement-1>
.
.
.
<statement-N>

In practice, the statements inside a class definition will usually be function definitions, but other statements are allowed, and sometimes useful — we’ll come back to this later. The function definitions inside a class normally have a peculiar form of argument list, dictated by the calling conventions for methods — again, this is explained later.

  • Process Behind Creation of Class in Python

When a class definition is entered, a new namespace is created, and used as the local scope — thus, all assignments to local variables go into this new namespace. In particular, function definitions bind the name of the new function here.

When a class definition is left normally (via the end), a class object is created. This is basically a wrapper around the contents of the namespace created by the class definition; we’ll learn more about class objects in the next section. The original local scope (the one in effect just before the class definition was entered) is reinstated, and the class object is bound here to the class name given in the class definition header (ClassName in the example).

Example:

class Dog:

……

……

Class Objects :

An object consists of :

  • State: It is represented by the attributes of an object. It also reflects the properties of an object.
  • Behavior: It is represented by the methods of an object. It also reflects the response of an object to other objects.
  • Identity: It gives a unique name to an object and enables one object to interact with other objects.

Example.

Declaring Objects (Also called instantiating a class)

Conceptual Example:

Detail Example :

class Person:
"This is a person class"
age = 10
def greet(self):
print('Hello')print(Person.age)

Output

10

Class objects support two kinds of operations:

attribute references and instantiation.

  1. Attribute references use the standard syntax used for all attribute references in Python: obj.name. Valid attribute names are all the names that were in the class’s namespace when the class object was created.

Example:

class MyClass:
“””A simple example class”””
i = 12345

def f(self):
return ‘hello world’

then MyClass.i and MyClass.f are valid attribute references, returning an integer and a function object, respectively. Class attributes can also be assigned to, so you can change the value of MyClass.i by assignment. __doc__ is also a valid attribute, returning the docstring belonging to the class: "A simple example class".

2.Class instantiation uses function notation. Just pretend that the class object is a parameter less function that returns a new instance of the class. For example (assuming the above class):

x = MyClass()

creates a new instance of the class and assigns this object to the local variable x.

The instantiation operation (“calling” a class object) creates an empty object. Many classes like to create objects with instances customized to a specific initial state. Therefore a class may define a special method named __init__(), like this:

def __init__(self):
self.data = []

When a class defines an __init__() method, class instantiation automatically invokes __init__() for the newly-created class instance. So in this example, a new, initialized instance can be obtained by:

x = MyClass()

Of course, the __init__() method may have arguments for greater flexibility. In that case, arguments given to the class instantiation operator are passed on to __init__(). For example,

>>>

>>> class Complex:
... def __init__(self, realpart, imagpart):
... self.r = realpart
... self.i = imagpart
...
>>> x = Complex(3.0, -4.5)
>>> x.r, x.i
(3.0, -4.5)

Conclusion :

References:

Python Classes and Objects — GeeksforGeeks

A class is a user-defined blueprint or prototype from which objects are created. Classes provide a means of bundling…

9. Classes — Python 3.9.5 documentation

Classes provide a means of bundling data and functionality together. Creating a new class creates a new type of object…

All about Pythonic Class: The Life Cycle

Python Data Model