Class is a collection of data (variables and methods). It bundles data and functionality together. It provides all standard features of object-oriented programming. Basically it is a blueprint for creating objects. Creating a new class creates a new type of object, allowing new instances of that type to be made.
Example:
# class 'A' defined class A(object): # Calling Constructor def __init__(self, a): self.a = a print("The value of a:", self.a) # Driver's code c = A(7) |
Output:
The value of a: 7
__subclasscheck__ in Python
__subclasscheck__ is one of the methods to customize the result of issubclass() built-in function. It is a method to check whether a class is a subclass or not and returns True if the class is considered as a subclass(direct or indirect) of another class, otherwise, returns False. It cannot be defined as a class method in the actual/real class. It is implemented in the metaclass, as it is not for ordinary classes. Consider the below example for better understanding.
Example: Consider a situation where you want to check if a certain value is present as an attribute inside a class using the issubclass() method.
# Python program to demonstrate # subclasscheck class A(type): # __subclasscheck__() defined def __subclasscheck__(cls, sub): # Getting the L attribute of # subclass attr = getattr(cls, 'L', []) # Checking if the subclass # is present in the L attribute # of subclass or not if sub in attr: return True return False class B(metaclass = A): # L Attribute L = [1, 2, 3, 4, 5] class C(metaclass = A): # L Attribute L = ["Geeks", "For"] # Driver's code print(issubclass(1, B)) print(issubclass("Geeks", B)) print(issubclass("Geeks", C)) |
Output:
True False True
__subclasshook__ in Python
Abstract class can override __subclasshook__() method to customize issubclass(). It returns True when a class is found to be subclass of a ABC class, it returns False if it is not and returns NotImplemented if the subclass check is continued with the usual mechanism. This method is defined in the ABC class with some conditions. Classes that follow those conditions are considered to be a subclass.
Note: It must be defined as a class method.
Example:
# Python program to demonstrate # subclasshook from abc import ABCMeta class A(metaclass = ABCMeta): @classmethod def __subclasshook__(cls, C): if cls is A: # condition to check if the # function anyfun() is present # in any sub class or not if any("__anyfun__" in Q.__dict__ for Q in C.__mro__): return True return False class P(object): pass class Q(object): def __anyfun__(self): return 0 # Driver's code print(issubclass(Q, A) ) print(issubclass(P, A) ) |
Output:
True False
