New submission from Raymond Hettinger:
Since inheritance is more commonplace and more easily understood than
__metaclass__, the abc module would benefit from a simple helper class:
class ABC(metaclass=ABCMeta):
pass
>From a user's point-of-view, writing an abstract base call becomes simpler and
>clearer:
from abc import ABC, abstractmethod
class Vector(ABC):
@abstractmethod
def __iter__(self):
pass
def dot(self, other):
'Compute a dot product'
return sum(map(operator.mul, self, other))
Notice that this class seems less mysterious because it inherits from ABC
rather than using __metaclass__=ABCMeta.
Also note, it has become a reasonably common practice for metaclass writers to
put the __metaclass__ assignment in a class and have it get inherited rather
than requiring users do the metaclass assignment themselves.
----------
components: Library (Lib)
messages: 171323
nosy: rhettinger
priority: normal
severity: normal
status: open
title: Create abstract base classes by inheritance rather than a direct
invocation of __metaclass__
versions: Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue16049>
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