Support iteration over enums with enum34 (#1412)

* Support iteration over enums in python 2

* fix lint

Author: ilinum

third_party/2/enum.pyi

@@ -1,7 +1,11 @@
-from typing import List, Any, TypeVar, Type
+from typing import List, Any, TypeVar, Type, Iterable, Iterator
 
-class Enum:
-    def __new__(cls, value: Any) -> None: ...
+_T = TypeVar('_T', bound=Enum)
+class EnumMeta(type, Iterable[Enum]):
+    def __iter__(self: Type[_T]) -> Iterator[_T]: ...  # type: ignore
+
+class Enum(metaclass=EnumMeta):
+    def __new__(cls: Type[_T], value: Any) -> _T: ...
     def __repr__(self) -> str: ...
     def __str__(self) -> str: ...
     def __dir__(self) -> List[str]: ...
@@ -12,8 +16,6 @@ class Enum:
     name = ...  # type: str
     value = ...  # type: Any
 
-_T = TypeVar('_T')
-
 class IntEnum(int, Enum):  # type: ignore
     def __new__(cls: Type[_T], value: Any) -> _T: ...