Difference abstract class and interface in Python

Question

How is abstract class different from interface in Python?

Answer 1

An interface, for an object, is a set of methods and attributes on that object.

In Python, we can use an abstract base class to define and enforce an interface.

For example, say we want to use one of the abstract base classes from the collections module:

import collections
class MySet(collections.Set):
    pass

If we try to use it, we get an TypeError because the class we created does not support the expected behavior of sets:

class ListBasedSet(collections.Set):
    """Alternate set implementation favoring space over speed
    and not requiring the set elements to be hashable. 
    """
    def __init__(self, iterable):
        self.elements = lst = []
        for value in iterable:
            if value not in lst:
                lst.append(value)
    def __iter__(self):
        return iter(self.elements)
    def __contains__(self, value):
        return value in self.elements
    def __len__(self):
        return len(self.elements)

s1 = ListBasedSet('abcdef')
s2 = ListBasedSet('defghi')
overlap = s1 & s2

There are other things we could do with this, like register virtual subclasses that already implement these interfaces, but I think that is beyond the scope of this question. The other methods demonstrated here would have to adapt this method using the abc module to do so, however.

Answer 2

If abstract class contains only abstract methods then it is interface.

abstract class can contain both abstract methods and concrete methods

Comments

I'm new to python and it would be helpful if you explained what concrete methods are. Thank you

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Hi @Harsh, A concrete method means, the method has a complete definition. but it can be overridden in the inherited class.