Parameter substitution in the union type does not work with typing.Union #88819
Comments
>>> import typing
>>> T = typing.TypeVar('T')
>>> (int | T)[typing.Union[str, list]]
NotImplementedSee also bpo-44633. But in this case the expected result is int | str | list or typing.Union[init, str, list]. |
serhiy-storchaka
added
3.10
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@serhiy, this doesn't just affect typing.Union, it seems that the rest of the typing types don't substitute: >>> (int | T)[typing.List[str]]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Each union arg must be a type, got typing.List[str]We should probably loosen the check during the union_getitem substitution -- no need to raise the TypeError or check for is_union, just blindly replace the TypeVar. We already do this for types.GenericAlias: >>> list[T][1]
list[1]Or if you want to continue checking, maybe checking for PyCallable_Check(obj) in substitution is enough - typing internally accepts callable(o) too: https://github.com/python/cpython/blob/3.10/Lib/typing.py#L146 |
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There is also problem with other typing types: >>> (int | T)[typing.List]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Each union argument must be a type, got typing.List
>>> (int | T)[typing.List[int]]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Each union argument must be a type, got typing.List[int]
>>> (int | T)[typing.Hashable]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Each union argument must be a type, got typing.Hashable
>>> (int | T)[typing.Callable[[int], str]]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Each union argument must be a type, got typing.Callable[[int], str]
>>> (int | T)[typing.ParamSpec('P')]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: Each union argument must be a type, got ~PDespite the fact that they support the | operator. We can add one by one special support of different types supporting the | operator (ParamSpec, _GenericAlias, _CallableGenericAlias, _UnionGenericAlias, _LiteralGenericAlias, _ConcatenateGenericAlias, _AnnotatedAlias, _SpecialGenericAlias, _CallableType, _TupleType), but it is cumbersome and errorprone. We will need to synchronize code of unionobject.c with typing every time we add new kind of types. PR 27247 uses more general approach. It calls the | operator for arguments after substitution. So all types which support the | operator are now automatically supported. But the result of parameter substitution can now be typing.Union instead of types.Union. >>> import typing
>>> import collections.abc
>>> T = typing.TypeVar('T')
>>> (int | T)[list]
int | list
>>> (int | T)[typing.List]
typing.Union[int, typing.List]
>>> (int | T)[list[int]]
int | list[int]
>>> (int | T)[typing.List[int]]
typing.Union[int, typing.List[int]]
>>> (int | T)[collections.abc.Hashable]
int | collections.abc.Hashable
>>> (int | T)[typing.Hashable]
typing.Union[int, typing.Hashable]
>>> (int | T)[collections.abc.Sequence[int]]
int | collections.abc.Sequence[int]
>>> (int | T)[typing.Sequence[int]]
typing.Union[int, typing.Sequence[int]]
>>> (int | T)[collections.abc.Callable[[int], str]]
int | collections.abc.Callable[[int], str]
>>> (int | T)[typing.Callable[[int], str]]
typing.Union[int, typing.Callable[[int], str]]
>>> (int | T)[typing.TypeVar('S')]
int | ~S
>>> (int | T)[typing.ParamSpec('P')]
typing.Union[int, ~P]
>>> (int | T)[str | list]
int | str | list
>>> (int | T)[typing.Union[str, list]]
typing.Union[int, str, list] |
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I need someone else to own this, sorry. |
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Thanks Serhiy for the report and the fix, and Ken for reviews. |
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Thanks for taking over here, Ł! |
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