bpo-46981: Remove typing._TypingEmpty (GH-31836)

serhiy-storchaka · web-flow · commit 15df8f8d89a0 · 2022-03-17T09:52:24.000+02:00
* get_args(Tuple[()]) now returns () instead of ((),).
* Tuple[Unpack[Ts]][()] now returns the result equal to Tuple[()].
diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
@@ -469,14 +469,12 @@ class G(Generic[Unpack[Ts]]): pass
 
         for A in G, Tuple:
             B = A[Unpack[Ts]]
-            if A != Tuple:
-                self.assertEqual(B[()], A[()])
+            self.assertEqual(B[()], A[()])
             self.assertEqual(B[float], A[float])
             self.assertEqual(B[float, str], A[float, str])
 
             C = List[A[Unpack[Ts]]]
-            if A != Tuple:
-                self.assertEqual(C[()], List[A[()]])
+            self.assertEqual(C[()], List[A[()]])
             self.assertEqual(C[float], List[A[float]])
             self.assertEqual(C[float, str], List[A[float, str]])
 
@@ -4248,7 +4246,7 @@ class C(Generic[T]): pass
         self.assertEqual(get_args(Union[int, Callable[[Tuple[T, ...]], str]]),
                          (int, Callable[[Tuple[T, ...]], str]))
         self.assertEqual(get_args(Tuple[int, ...]), (int, ...))
-        self.assertEqual(get_args(Tuple[()]), ((),))
+        self.assertEqual(get_args(Tuple[()]), ())
         self.assertEqual(get_args(Annotated[T, 'one', 2, ['three']]), (T, 'one', 2, ['three']))
         self.assertEqual(get_args(List), ())
         self.assertEqual(get_args(Tuple), ())
diff --git a/Lib/typing.py b/Lib/typing.py
@@ -1220,7 +1220,6 @@ def __init__(self, origin, args, *, inst=True, name=None,
         if not isinstance(args, tuple):
             args = (args,)
         self.__args__ = tuple(... if a is _TypingEllipsis else
-                              () if a is _TypingEmpty else
                               a for a in args)
         self.__parameters__ = _collect_parameters(args)
         self._paramspec_tvars = _paramspec_tvars
@@ -1503,8 +1502,6 @@ def __getitem_inner__(self, params):
 class _TupleType(_SpecialGenericAlias, _root=True):
     @_tp_cache
     def __getitem__(self, params):
-        if params == ():
-            return self.copy_with((_TypingEmpty,))
         if not isinstance(params, tuple):
             params = (params,)
         if len(params) >= 2 and params[-1] is ...:
@@ -1735,13 +1732,6 @@ def __init_subclass__(cls, *args, **kwargs):
         cls.__parameters__ = tuple(tvars)
 
 
-class _TypingEmpty:
-    """Internal placeholder for () or []. Used by TupleMeta and CallableMeta
-    to allow empty list/tuple in specific places, without allowing them
-    to sneak in where prohibited.
-    """
-
-
 class _TypingEllipsis:
     """Internal placeholder for ... (ellipsis)."""
 
diff --git a/Misc/NEWS.d/next/Library/2022-03-12-11-30-42.bpo-46981.ltWCxH.rst b/Misc/NEWS.d/next/Library/2022-03-12-11-30-42.bpo-46981.ltWCxH.rst
@@ -0,0 +1,2 @@
+``typing.get_args(typing.Tuple[()])`` now returns ``()`` instead of
+``((),)``.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+``typing.get_args(typing.Tuple[()])`` now returns ``()`` instead of
	`2`	+``((),)``.