Comments (7)
Yes, the allowed forms for base classes and the idioms to use for various
cases are not yet sorted out. I also don't like that mypy has both
Generic[T] and AbstractGeneric[T].
On Wed, Jan 14, 2015 at 11:09 PM, Jukka Lehtosalo [email protected]
wrote:
The PEP should probably mention what happens if a generic class is used as
a base class.Examples to consider:
class StrList(List[str]): ... # StrList is not generic
T = TypeVar('T')
class MyList(List[T]): ... # Mypy requires Generic[T] as a base class, but it's ugly
x = Undefined(MyList[int])
—
Reply to this email directly or view it on GitHub
#41.
--Guido van Rossum (python.org/~guido)
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See also https://github.com/JukkaL/typing/issues/36 about Generic
and AbstractGeneric
.
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Currently this is not valid (due to Python semantics):
class A(metaclass=ABCMeta): pass
class B(Generic[T], A): pass # metaclass conflict
This is okay, however:
class A(metaclass=ABCMeta): pass
class B(AbstractGeneric[T], A): pass # good
Maybe we should just replace Generic
with AbstractGeneric
and remove AbstractGeneric
? This way most reasonable inheritance patterns should work okay. With the current mypy approach, inheritance hierarchies are inherently fragile -- if some base class adds ABCMeta
as metaclass (due to adding an abstract base class, for example), it can break subclasses that are generic.
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So, what shall we do? If at all possible I'd like to only have Generic
.
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I updated mypy and typing to only have Generic
, which also supports defining ABCs. It seems to be okay to me, but I need to do more testing.
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Added section 'Arbitrary generic types as base classes' to the PEP. Not closing this issue this yet until somebody has reviewed it.
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Everything looks good to me, except for #85.
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