Abstract Method

Abstract Method is a method that should be redefined in subclasses.

To create an abstract method, you should import the @abstractmethod decorator from the abc library.

Note

Pay attention: decorator is imported without the @ symbol.


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from abc import ABC, abstractmethod

class SomeClass(ABC):
    @abstractmethod
    def some_method():
        pass

instance = SomeClass()  # TypeError

The abstract methods should be implemented in subclasses. You can't create a subclass without redefining all abstract methods:


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from abc import ABC, abstractmethod

class AbstractParent(ABC):
    @abstractmethod
    def first_method():
        pass
    
    @abstractmethod
    def second_method():
        pass

class Child(AbstractParent):
    def first_method(self):
        print("The first method")

instance = Child()  # TypeError

The class Child saved the Abstract Class state because the second_method is not redefined, and the ABC class exists in the inheritance hierarchy.


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from abc import ABC, abstractmethod

class AbstractParent(ABC):
    @abstractmethod
    def first_method():
        pass
    
    @abstractmethod
    def second_method():
        pass

class Child(AbstractParent):
    def first_method(self):
      print("The first method")

    def second_method(self):
        print("The second method")


instance = Child()
instance.first_method()
instance.second_method()

Note

The abstract classes and methods exist to provide a strict class structure.

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Section 4. Chapter 6