Python – Difference between abstract class and interface in Python


What is the difference between abstract class and interface in Python?

Best Solution

What you'll see sometimes is the following:

class Abstract1:
    """Some description that tells you it's abstract,
    often listing the methods you're expected to supply."""

    def aMethod(self):
        raise NotImplementedError("Should have implemented this")

Because Python doesn't have (and doesn't need) a formal Interface contract, the Java-style distinction between abstraction and interface doesn't exist. If someone goes through the effort to define a formal interface, it will also be an abstract class. The only differences would be in the stated intent in the docstring.

And the difference between abstract and interface is a hairsplitting thing when you have duck typing.

Java uses interfaces because it doesn't have multiple inheritance.

Because Python has multiple inheritance, you may also see something like this

class SomeAbstraction:
    pass  # lots of stuff - but missing something

class Mixin1:
    def something(self):
        pass  # one implementation

class Mixin2:
    def something(self):
        pass  # another

class Concrete1(SomeAbstraction, Mixin1):

class Concrete2(SomeAbstraction, Mixin2):

This uses a kind of abstract superclass with mixins to create concrete subclasses that are disjoint.