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Use TypeGuard for has in Python 3.10 and above #997

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merged 8 commits into from Aug 16, 2022
Merged

Use TypeGuard for has in Python 3.10 and above #997

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4e9f892
Use `TypeGuard` for `has` in Python 3.10 and above
layday Aug 8, 2022
06ee0a8
Merge branch 'main' into add-has-typeguard
hynek Aug 10, 2022
d824f72
Merge branch 'main' into add-has-typeguard
hynek Aug 11, 2022
fd2c819
fixup! Use `TypeGuard` for `has` in Python 3.10 and above
layday Aug 15, 2022
eacdd81
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Aug 15, 2022
f8c2e04
Test the negative case
layday Aug 15, 2022
266f10d
Add type guard example
layday Aug 15, 2022
26a8d5e
Merge branch 'main' into add-has-typeguard
hynek Aug 16, 2022
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10 changes: 9 additions & 1 deletion src/attr/__init__.pyi
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Expand Up @@ -470,7 +470,15 @@ def astuple(
tuple_factory: Type[Sequence[Any]] = ...,
retain_collection_types: bool = ...,
) -> Tuple[Any, ...]: ...
def has(cls: type) -> bool: ...

if sys.version_info >= (3, 10):
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Would it be feasible to add a conditional import from typing-extensions?

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You can only use one of a small number of constants like TYPE_CHECKING and sys.version_info to define types conditionally, try/except won't work, so I don't think so.

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In my very limited testing this seems to work, both in Mypy and Pyright:

Screenshot 2022-08-15 at 13 37 05

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Right, but typing_extensions is not a dependency of attrs, so that'll error if typing_extensions is not installed.

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@layday layday Aug 15, 2022 •
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Okay, it seems typeshed ships typing_extensions as part of the stdlib, so I guess we can actually do that.

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Done in fd2c819.

from typing import TypeGuard

def has(cls: type) -> TypeGuard[Type[AttrsInstance]]: ...

else:
def has(cls: type) -> bool: ...

def assoc(inst: _T, **changes: Any) -> _T: ...
def evolve(inst: _T, **changes: Any) -> _T: ...

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12 changes: 12 additions & 0 deletions tests/test_mypy.yml
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Expand Up @@ -1371,3 +1371,15 @@
b: str

fields(A) # E: Argument 1 to "fields" has incompatible type "Type[A]"; expected "Type[AttrsInstance]"

- case: testHasTypeGuard
skip: sys.version_info < (3, 10)
main: |
from attrs import define, has

@define
class A:
pass

if has(A):
reveal_type(A) # N: Revealed type is "Type[attr.AttrsInstance]"