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Use overloading rather than Union for MutableMapping.update (#174)

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See https://github.com/python/mypy/issues/1430 for motivation.
This commit is contained in:
rwbarton
2016-05-01 09:50:01 -07:00
committed by Jukka Lehtosalo
parent a5d5dcc4f4
commit 2b80cdf75e
6 changed files with 34 additions and 14 deletions
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16
stdlib/3/typing.pyi
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@@ -236,8 +236,20 @@ class MutableMapping(Mapping[_KT, _VT], Generic[_KT, _VT]):
def pop(self, k: _KT, default: _VT = ...) -> _VT: ...
def popitem(self) -> Tuple[_KT, _VT]: ...
def setdefault(self, k: _KT, default: _VT = ...) -> _VT: ...
def update(self, m: Union[Mapping[_KT, _VT],
Iterable[Tuple[_KT, _VT]]]) -> None: ...
# 'update' used to take a Union, but using overloading is better.
# The second overloaded type here is a bit too general, because
# Mapping[Tuple[_KT, _VT], W] is a subclass of Iterable[Tuple[_KT, _VT]],
# but will always have the behavior of the first overloaded type
# at runtime, leading to keys of a mix of types _KT and Tuple[_KT, _VT].
# We don't currently have any way of forcing all Mappings to use
# the first overload, but by using overloading rather than a Union,
# mypy will commit to using the first overload when the argument is
# known to be a Mapping with unknown type parameters, which is closer
# to the behavior we want. See mypy issue #1430.
@overload
def update(self, m: Mapping[_KT, _VT]) -> None: ...
@overload
def update(self, m: Iterable[Tuple[_KT, _VT]]) -> None: ...
Text = str