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builtins.sum: Add overload for bool special case #7975

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JelleZijlstra merged 3 commits into from
May 28, 2022
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builtins.sum: Add overload for bool special case #7975

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`builtins.sum`: Add overload for `bool` special case
AlexWaygood May 28, 2022
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I know the overloads overlap
AlexWaygood May 28, 2022
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AlexWaygood May 28, 2022
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12 changes: 12 additions & 0 deletions stdlib/builtins.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -1548,6 +1548,18 @@ def sorted(__iterable: Iterable[_T], *, key: Callable[[_T], SupportsRichComparis
_SumT = TypeVar("_SumT", bound=SupportsAdd)
_SumS = TypeVar("_SumS", bound=SupportsAdd)

# In general, the return type of `x + x` is *not* guaranteed to be the same type as x.
# However, we can't express that in the stub for `sum()`
# without creating many false-positive errors (see #7578).
# Instead, we special-case the most common example of this: bool.
if sys.version_info >= (3, 8):
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@overload
def sum(__iterable: Iterable[bool], start: int = ...) -> int: ... # type: ignore[misc]

else:
@overload
def sum(__iterable: Iterable[bool], __start: int = ...) -> int: ... # type: ignore[misc]

@overload
def sum(__iterable: Iterable[_SumT]) -> _SumT | Literal[0]: ...

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