Ivan Levkivskyi <[email protected]> added the comment:
> So why is it bad that in the example class B is considered a "subclass" of
> os.PathLike by implementing the protocol?
This is not bad, my understanding of the problem is that currently B is
considered a subclass of A, while the latter should not be structural.
To give an analogy with PEP 544 (sorry, this is my favourite one :-)) consider
this:
class P(Protocol):
def some(self): ...
class C:
def some(self): ...
Here C is obviously a "subclass" of P, but:
class Bad(P): # <- this is _no_ a protocol, just a nominal class
pass # explicitly subclassing P
class Good(P, Protocol): # <- this is a subprotocol that
pass # happened to be identical to P
So here C is a "subclass" of Good, but not a "subclass" of Bad.
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<https://bugs.python.org/issue38878>
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