Is there any difference between using ABC vs ABCMeta?

Question

In Python 3.4+, we can do

class Foo(abc.ABC):     ... 

or we can do

class Foo(metaclass=abc.ABCMeta):     ... 

Are there any differences between the two that I should be aware of?

Answer 1

abc.ABC basically just an extra layer over metaclass=abc.ABCMeta. i.e abc.ABC implicitly defines the metaclass for us.

(Source: https://hg.python.org/cpython/file/3.4/Lib/abc.py#l234)

class ABC(metaclass=ABCMeta):     """Helper class that provides a standard way to create an ABC using     inheritance.     """     pass 

The only difference is that in the former case you need a simple inheritance and in the latter you need to specify the metaclass.

From What's new in Python 3.4(emphasis mine):

New class ABC has ABCMeta as its meta class. Using ABC as a base class has essentially the same effect as specifying metaclass=abc.ABCMeta, but is simpler to type and easier to read.

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Related issue: Create abstract base classes by inheritance rather than a direct invocation of __metaclass__