From e33390bf2901c812216ed5462d5f78855b41545f Mon Sep 17 00:00:00 2001
From: Travis J Parker <travis.parker@gmail.com>
Date: Tue, 29 Aug 2017 13:25:52 -0700
Subject: [PATCH] Correct return type of sum() builtin

`sum([])` always returns the integer 0.
---
 stdlib/2/__builtin__.pyi | 5 ++++-
 stdlib/3/builtins.pyi    | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/stdlib/2/__builtin__.pyi b/stdlib/2/__builtin__.pyi
index b781292ec2b6..0b8dfb1b3b19 100644
--- a/stdlib/2/__builtin__.pyi
+++ b/stdlib/2/__builtin__.pyi
@@ -789,7 +789,10 @@ def sorted(iterable: Iterable[_T], *,
            cmp: Callable[[_T, _T], int] = ...,
            key: Callable[[_T], Any] = ...,
            reverse: bool = ...) -> List[_T]: ...
-def sum(iterable: Iterable[_T], start: _T = ...) -> _T: ...
+@overload
+def sum(iterable: Iterable[_T]) -> Union[_T, int]: ...
+@overload
+def sum(iterable: Iterable[_T], start: _S) -> Union[_T, _S]: ...
 def unichr(i: int) -> unicode: ...
 def vars(object: Any = ...) -> Dict[str, Any]: ...
 @overload
diff --git a/stdlib/3/builtins.pyi b/stdlib/3/builtins.pyi
index 80fc8e50969f..3f65e90f9df0 100644
--- a/stdlib/3/builtins.pyi
+++ b/stdlib/3/builtins.pyi
@@ -866,7 +866,10 @@ def setattr(object: Any, name: str, value: Any) -> None: ...
 def sorted(iterable: Iterable[_T], *,
            key: Optional[Callable[[_T], Any]] = None,
            reverse: bool = False) -> List[_T]: ...
-def sum(iterable: Iterable[_T], start: _T = ...) -> _T: ...
+@overload
+def sum(iterable: Iterable[_T]) -> Union[_T, int]: ...
+@overload
+def sum(iterable: Iterable[_T], start: _S) -> Union[_T, _S]: ...
 def vars(object: Any = ...) -> Dict[str, Any]: ...
 @overload
 def zip(iter1: Iterable[_T1]) -> Iterator[Tuple[_T1]]: ...