From 18b506e6a41dcf8d947802d74ef983f616c6b2e9 Mon Sep 17 00:00:00 2001
From: Guido van Rossum <guido@dropbox.com>
Date: Thu, 15 Sep 2016 16:31:46 -0700
Subject: [PATCH] Better signature for Mapping.get().

Fixes #278.

The approach here is different from what we thought before.  According
to this commit, there are three valid forms of Mapping[K, V].get():

  d.get()      # returns Optional[V]
  d.get(None)  # also returns Optional[V]  (seen in the wild)
  d.get(v)     # requires v to have type V, and returns V

So we don't allow d.get(d) where d is a type unrelated to V.  This is
a compromise, but I don't think there's much use for d.get(d) with a
default that is differently-typed than V, and when I tried it my
application code (that didn't use this) wouldn't type-check correctly.
---
 stdlib/2.7/UserDict.pyi    | 7 +++++--
 stdlib/2.7/__builtin__.pyi | 6 +++++-
 stdlib/2.7/typing.pyi      | 6 +++++-
 stdlib/3/builtins.pyi      | 5 ++++-
 stdlib/3/typing.pyi        | 6 +++++-
 5 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/stdlib/2.7/UserDict.pyi b/stdlib/2.7/UserDict.pyi
index 10525fe116cc..fc9e15b796cf 100644
--- a/stdlib/2.7/UserDict.pyi
+++ b/stdlib/2.7/UserDict.pyi
@@ -1,5 +1,5 @@
 from typing import (Any, Container, Dict, Generic, Iterable, Iterator, List,
-                    Mapping, Sized, Tuple, TypeVar, overload)
+                    Mapping, Optional, Sized, Tuple, TypeVar, overload)
 
 _KT = TypeVar('_KT')
 _VT = TypeVar('_VT')
@@ -19,7 +19,10 @@ class DictMixin(Sized, Iterable[_KT], Container[_KT], Generic[_KT, _VT]):
 
     # From  typing.Mapping[_KT, _VT]
     # (can't inherit because of keys())
-    def get(self, k: _KT, default: _VT = ...) -> _VT: ...
+    @overload
+    def get(self, k: _KT, default: Optional[None] = ...) -> Optional[_VT]: ...
+    @overload
+    def get(self, k: _KT, default: _VT) -> _VT: ...
     def values(self) -> List[_VT]: ...
     def items(self) -> List[Tuple[_KT, _VT]]: ...
     def iterkeys(self) -> Iterator[_KT]: ...
diff --git a/stdlib/2.7/__builtin__.pyi b/stdlib/2.7/__builtin__.pyi
index e47720477ee8..d4e41b7f9a76 100644
--- a/stdlib/2.7/__builtin__.pyi
+++ b/stdlib/2.7/__builtin__.pyi
@@ -532,7 +532,11 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     def has_key(self, k: _KT) -> bool: ...
     def clear(self) -> None: ...
     def copy(self) -> Dict[_KT, _VT]: ...
-    def get(self, k: _KT, default: _VT = None) -> _VT: ...
+    @overload
+    def get(self, k: _KT, default: Optional[None] = ...) -> Optional[_VT]:
+        ...
+    @overload
+    def get(self, k: _KT, default: _VT) -> _VT: ...
     def pop(self, k: _KT, default: _VT = ...) -> _VT: ...
     def popitem(self) -> Tuple[_KT, _VT]: ...
     def setdefault(self, k: _KT, default: _VT = ...) -> _VT: ...
diff --git a/stdlib/2.7/typing.pyi b/stdlib/2.7/typing.pyi
index 90a22292df24..9415e2aebc08 100644
--- a/stdlib/2.7/typing.pyi
+++ b/stdlib/2.7/typing.pyi
@@ -180,7 +180,11 @@ class Mapping(Sized, Iterable[_KT], Container[_KT], Generic[_KT, _VT_co]):
     def __getitem__(self, k: _KT) -> _VT_co:
         ...
     # Mixin methods
-    def get(self, k: _KT, default: _VT_co = ...) -> _VT_co:  # type: ignore
+    @overload
+    def get(self, k: _KT, default: Optional[None] = ...) -> Optional[_VT_co]:  # type: ignore
+        ...
+    @overload  # type: ignore
+    def get(self, k: _KT, default: _VT_co) -> _VT_co:  # type: ignore
         ...
     def keys(self) -> list[_KT]: ...
     def values(self) -> list[_VT_co]: ...
diff --git a/stdlib/3/builtins.pyi b/stdlib/3/builtins.pyi
index 774b90808605..bf18d5601c24 100644
--- a/stdlib/3/builtins.pyi
+++ b/stdlib/3/builtins.pyi
@@ -517,7 +517,10 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     def __init__(self, iterable: Iterable[Tuple[_KT, _VT]], **kwargs: _VT) -> None: ...
     def clear(self) -> None: ...
     def copy(self) -> Dict[_KT, _VT]: ...
-    def get(self, k: _KT, default: _VT = None) -> _VT: ...
+    @overload
+    def get(self, k: _KT, default: Optional[None] = ...) -> Optional[_VT]: ...
+    @overload
+    def get(self, k: _KT, default: _VT) -> _VT: ...
     def pop(self, k: _KT, default: _VT = None) -> _VT: ...
     def popitem(self) -> Tuple[_KT, _VT]: ...
     def setdefault(self, k: _KT, default: _VT = None) -> _VT: ...
diff --git a/stdlib/3/typing.pyi b/stdlib/3/typing.pyi
index 9629020a366d..ab5172f0eef9 100644
--- a/stdlib/3/typing.pyi
+++ b/stdlib/3/typing.pyi
@@ -230,7 +230,11 @@ class Mapping(Iterable[_KT], Container[_KT], Sized, Generic[_KT, _VT_co]):
     def __getitem__(self, k: _KT) -> _VT_co:
         ...
     # Mixin methods
-    def get(self, k: _KT, default: _VT_co = ...) -> _VT_co:  # type: ignore
+    @overload
+    def get(self, k: _KT, default: Optional[None] = ...) -> Optional[_VT_co]:  # type: ignore
+        ...
+    @overload  # type: ignore
+    def get(self, k: _KT, default: _VT_co) -> _VT_co:  # type: ignore
         ...
     def items(self) -> AbstractSet[Tuple[_KT, _VT_co]]: ...
     def keys(self) -> AbstractSet[_KT]: ...