Classes and Objects in Python OOP

1. About Python classes and objects

Haven't you thought that you used and still use OOP all the time without realizing it?
Even using other paradigms in Python, you still use objects to do almost everything.
This is because, in Python, everything is an object.
Remember the definition of an object: An object in Python is a unique collection of data (attributes) and behaviors (methods).
This matches any data type in Python.
Let's take a simple example: a simple character string is an object which has properties (attributes) and methods (upper(), lower(), center(), count() etc…). As you see in the figure below:

The same goes for integers, floats, booleans, lists and dictionaries etc.
In general, a class in OOP is a code model from which we create what are called objects (we also say instances or instance objects)

2. Classes in Python

To create a class in Python, we use the instruction:

class name_of_the_class

We then create a method that allows us to build the objects, called constructor via the instruction:

# define the class constructor
def __init__(self):
    ...

Example. Person class

class Person:
    
    # define the class constructor
    def __init__(self,name,age):
        self.name = name # define the name attribute
        self.age = age # define the age attribute
# creating of an instance object        
P = Person("Albert",27)

# display instance attributes
print("The person's name is: ", P.name)
print("The person's age is: " , P.age, " years")
"""
output: 
The person's name is: 'Albert'
The person's age is: '27 years'
"""

Example. Rectangle class

class Rectangle:
    
    # define the class constructor
    def __init__(self,L,l):
        self.Length=L # define the Length attribute
        self.Width=l # define the Width attribute
# creating of an instance object        
myRectangle=Rectangle(7,5)

# display the the instance attributes
print("The length of my rectangle is: ",myRectangle.Length)
print("The width of my rectangle is: ",myRectangle.Width)
"""
output:
The length of my rectangle is:  7
The width of my rectangle is:  5
"""

3. Instance methods in Python

Definition An instance method is any named method or procedure within the class, allowing to define properties or behaviors of instance objects. An instance method has one or more parameters, the first parmeter must be named self!

Example. adding an instance method that calculates the area of ​​the rectangle

class Rectangle:
    def __init__(self,L,l):
        self.Length=L
        self.Width=l

    # instance method that calculates area
    def area(self):
        return self.Length*self.Width

# create a rectangle of length 7 and width 5
myRectangle = Rectangle(7.5)
print("The area of ​​my rectangle is: ", myRectangle.area())
# output: The area of ​​my rectangle is: 35

4. Class methods in Python

A class method in Python is a method that works within the class where it was created and it is accessible by an instance object or directly by using the class name without doing any instantiation! A class method is characterized by:

5. Instance attributes and class attributes

An instance attribute is an attribute that works with an instance object while a class attribute is an attribute that works with the class

Example 1. instance attributes & class attributes

class Student:
    name = 'Aladdin' # class attribute
    def __init__(self):
        self.age = 30 # instance attribute

    @classmethod
    def displayName(cls):
        print("Student name is:", cls.name)

# we can use the class method without doing any instantiation !        
print(Student.displayName())# output: Student name is: Aladdin

# the class method can also used by an instance object
Stud = Student()
print(Stud.displayName())# output: Student name is: Aladdin

6. Static methods

Static methods, work like class methods, are methods that are bound to a class rather than its object.
statics methods can be executed without going through instantiation

Example. static method

class myClass:
    def __init__(self):
        pass

    # create a static method
    @staticmethod
    def myStaticMethod():
        print("Here is an example of a static method in Python")

myClass.myStaticMethod()
# output: 'Here is an example of a static method in Python'

Younes Derfoufi
my-courses.net