How does polymorphism work in Python?

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The is operator in Python checks that the two arguments refer to the same object in memory; it is not like the is operator in C#.

From the docs:

The operators is and is not test for object identity: x is y is true if and only if x and y are the same object. x is not y yields the inverse truth value.

What you’re looking for in this case is isinstance.

Return true if the object argument is an instance of the classinfo argument, or of a (direct or indirect) subclass thereof. 

>>> class animal(object): pass

>>> class dog(animal): pass

>>> myDog = dog()
>>> isinstance(myDog, dog)
True
>>> isinstance(myDog, animal)
True

However, idiomatic Python dictates that you (almost) never do type-checking, but instead rely on duck-typing for polymorphic behavior. There’s nothing wrong with using isinstance to understand inheritance, but it should generally be avoided in “production” code.

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