Add DictMixin, IterableUserDict to 2.7/UserDict (#513)

stdlib/2.7/UserDict.pyi

@@ -1,4 +1,5 @@
-from typing import Dict, Generic, Mapping, TypeVar
+from typing import (Any, Container, Dict, Generic, Iterable, Iterator, List,
+                    Mapping, Sized, Tuple, TypeVar, overload)
 
 _KT = TypeVar('_KT')
 _VT = TypeVar('_VT')
@@ -8,4 +9,30 @@ class UserDict(Dict[_KT, _VT], Generic[_KT, _VT]):
 
     def __init__(self, initialdata: Mapping[_KT, _VT] = ...) -> None: ...
 
-    # TODO: DictMixin
+    # TODO: __iter__ is not available for UserDict
+
+class IterableUserDict(UserDict[_KT, _VT], Generic[_KT, _VT]):
+    ...
+
+class DictMixin(Sized, Iterable[_KT], Container[_KT], Generic[_KT, _VT]):
+    def has_key(self, key: _KT) -> bool: ...
+
+    # From  typing.Mapping[_KT, _VT]
+    # (can't inherit because of keys())
+    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]: ...
+    def itervalues(self) -> Iterator[_VT]: ...
+    def iteritems(self) -> Iterator[Tuple[_KT, _VT]]: ...
+    def __contains__(self, o: Any) -> bool: ...
+
+    # From typing.MutableMapping[_KT, _VT]
+    def clear(self) -> None: ...
+    def pop(self, k: _KT, default: _VT = ...) -> _VT: ...
+    def popitem(self) -> Tuple[_KT, _VT]: ...
+    def setdefault(self, k: _KT, default: _VT = ...) -> _VT: ...
+    @overload
+    def update(self, m: Mapping[_KT, _VT], **kwargs: _VT) -> None: ...
+    @overload
+    def update(self, m: Iterable[Tuple[_KT, _VT]], **kwargs: _VT) -> None: ...