How is a variable declared inside a class?

In Python, a variable inside a class is declared either as a class attribute or as an instance attribute.

• A class attribute is declared directly within the class body and is shared among all instances:

class MyClass:
    class_variable = 10  # class attribute

• An instance attribute is declared inside a method, usually in the constructor __init__, and belongs to a specific object:

class MyClass:
    def __init__(self, value):
        self.instance_variable = value  # instance attribute

Thus, declaring a variable inside a class depends on whether a common attribute for all objects is needed or an individual one for each instance.