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Narrower typing on Factory called with takes_self #780

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Mar 24, 2021
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33 changes: 26 additions & 7 deletions src/attr/__init__.pyi
Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
import sys

from typing import (
Any,
Callable,
Expand Down Expand Up @@ -60,13 +62,30 @@ NOTHING: object
# NOTE: Factory lies about its return type to make this possible:
# `x: List[int] # = Factory(list)`
# Work around mypy issue #4554 in the common case by using an overload.
@overload
def Factory(factory: Callable[[], _T]) -> _T: ...
@overload
def Factory(
factory: Union[Callable[[Any], _T], Callable[[], _T]],
takes_self: bool = ...,
) -> _T: ...
if sys.version_info >= (3, 8):
from typing import Literal

@overload
def Factory(factory: Callable[[], _T]) -> _T: ...
@overload
def Factory(
factory: Callable[[Any], _T],
takes_self: Literal[True],
) -> _T: ...
@overload
def Factory(
factory: Callable[[], _T],
takes_self: Literal[False],
) -> _T: ...
else:
@overload
def Factory(factory: Callable[[], _T]) -> _T: ...
@overload
def Factory(
factory: Union[Callable[[Any], _T], Callable[[], _T]],
takes_self: bool = ...,
) -> _T: ...


class Attribute(Generic[_T]):
name: str
Expand Down
7 changes: 7 additions & 0 deletions tests/typing_example.py
Original file line number Diff line number Diff line change
Expand Up @@ -250,3 +250,10 @@ class NGFrozen:
@attr.s(collect_by_mro=True)
class MRO:
pass


@attr.s
class FactoryTest:
a: List[int] = attr.ib(default=attr.Factory(list))
b: List[Any] = attr.ib(default=attr.Factory(list, False))
c: List[int] = attr.ib(default=attr.Factory((lambda s: s.a), True))