Merge pull request #357 from hcarty/typing-types-and-exhaustiveness

Add typing.(TypeAlias, NewType, Never, assert_never) for type checkers

python/typing.py

@@ -24,6 +24,8 @@ Union = _PLACEHOLDER
 Optional = _PLACEHOLDER
 Callable = _PLACEHOLDER
 Type = _PLACEHOLDER
+TypeAlias = _PLACEHOLDER
+NewType = _PLACEHOLDER
 
 Literal = _PLACEHOLDER
 LiteralString = _PLACEHOLDER
@@ -39,9 +41,13 @@ Self = _PLACEHOLDER
 
 Protocol = object
 Generic = object
+Never = object
 
 TYPE_CHECKING = False
 
 # decorators
 overload = lambda x: x
 final = lambda x: x
+
+# exhaustiveness checking
+assert_never = lambda x: x