Create mypy.typing module for experimental typing additions. Move TypedDict there.

Author: davidfstr

mypy/semanal.py

@@ -1812,7 +1812,7 @@ def check_typeddict(self, node: Node, var_name: str = None) -> TypeInfo:
             return None
         callee = call.callee
         fullname = callee.fullname
-        if fullname != 'typing.TypedDict':
+        if fullname != 'mypy.typing.TypedDict':
             return None
         items, types, ok = self.parse_typeddict_args(call, fullname)
         if not ok:

mypy/typing.py

@@ -0,0 +1,22 @@
+"""The "mypy.typing" module defines experimental extensions to the standard
+"typing" module that is supported by the mypy typechecker.
+"""
+
+from typing import cast, Dict, Type, TypeVar
+
+
+_T = TypeVar('_T')
+
+
+def TypedDict(typename: str, fields: Dict[str, Type[_T]]) -> Type[dict]:
+    """TypedDict creates a dictionary type that expects all of its
+    instances to have a certain common set of keys, with each key
+    associated with a value of a consistent type. This expectation
+    is not checked at runtime but is only enforced by typecheckers.
+    """
+    def new_dict(*args, **kwargs):
+        return dict(*args, **kwargs)
+    
+    new_dict.__name__ = typename  # type: ignore  # https://github.com/python/mypy/issues/708
+    new_dict.__supertype__ = dict  # type: ignore  # https://github.com/python/mypy/issues/708
+    return cast(Type[dict], new_dict)

test-data/unit/semanal-typeddict.test

@@ -1,12 +1,7 @@
 -- Semantic analysis of typed dicts
 
 [case testCanDefineTypedDictType]
-# TODO: Support TypedDict in typing.py and not just typing.pyi
-from typing import TYPE_CHECKING
-if TYPE_CHECKING:
-    from typing import TypedDict
-else:
-    TypedDict = lambda name, fields: dict
+from mypy.typing import TypedDict
 Point = TypedDict('Point', {'x': int, 'y': int})
 [out]
 ...
@@ -15,12 +10,7 @@ Point = TypedDict('Point', {'x': int, 'y': int})
 
 -- TODO: Support: testCanAnnotateDictLiteralAsTypedDict
 [case testCannotYetAnnotateDictLiteralAsTypedDict]
-# TODO: Support TypedDict in typing.py and not just typing.pyi
-from typing import TYPE_CHECKING
-if TYPE_CHECKING:
-    from typing import TypedDict
-else:
-    TypedDict = lambda name, fields: dict
+from mypy.typing import TypedDict
 Point = TypedDict('Point', {'x': int, 'y': int})
-point = dict(x=42, y=1337) # type: Point # E: Incompatible types in assignment (expression has type Dict[str, int], variable has type "Point")
+point = dict(x=42, y=1337)  # type: Point  # E: Incompatible types in assignment (expression has type Dict[str, int], variable has type "Point")