bpo-44791: Accept ellipsis as the last argument of typing.Concatenate (…

…#30969)

Doc/library/typing.rst

@@ -852,7 +852,8 @@ These can be used as types in annotations using ``[]``, each having a unique syn
  callable. Usage is in the form
  ``Concatenate[Arg1Type, Arg2Type, ..., ParamSpecVariable]``. ``Concatenate``
  is currently only valid when used as the first argument to a :data:`Callable`.
- The last parameter to ``Concatenate`` must be a :class:`ParamSpec`.
+ The last parameter to ``Concatenate`` must be a :class:`ParamSpec` or
+ ellipsis (``...``).
 
  For example, to annotate a decorator ``with_lock`` which provides a
  :class:`threading.Lock` to the decorated function, ``Concatenate`` can be

Lib/test/test_typing.py

@@ -1755,8 +1755,7 @@ def test_concatenate(self):
  self.assertEqual(C[[], int], Callable[[int], int])
  self.assertEqual(C[Concatenate[str, P2], int],
  Callable[Concatenate[int, str, P2], int])
- with self.assertRaises(TypeError):
- C[..., int]
+ self.assertEqual(C[..., int], Callable[Concatenate[int, ...], int])
 
  C = Callable[Concatenate[int, P], int]
  self.assertEqual(repr(C),
@@ -1767,8 +1766,7 @@ def test_concatenate(self):
  self.assertEqual(C[[]], Callable[[int], int])
  self.assertEqual(C[Concatenate[str, P2]],
  Callable[Concatenate[int, str, P2], int])
- with self.assertRaises(TypeError):
- C[...]
+ self.assertEqual(C[...], Callable[Concatenate[int, ...], int])
 
  def test_errors(self):
  Callable = self.Callable
@@ -6739,17 +6737,15 @@ def test_var_substitution(self):
  self.assertEqual(C[int, []], (int,))
  self.assertEqual(C[int, Concatenate[str, P2]],
  Concatenate[int, str, P2])
- with self.assertRaises(TypeError):
- C[int, ...]
+ self.assertEqual(C[int, ...], Concatenate[int, ...])
 
  C = Concatenate[int, P]
  self.assertEqual(C[P2], Concatenate[int, P2])
  self.assertEqual(C[[str, float]], (int, str, float))
  self.assertEqual(C[str, float], (int, str, float))
  self.assertEqual(C[[]], (int,))
  self.assertEqual(C[Concatenate[str, P2]], Concatenate[int, str, P2])
- with self.assertRaises(TypeError):
- C[...]
+ self.assertEqual(C[...], Concatenate[int, ...])
 
 class TypeGuardTests(BaseTestCase):
  def test_basics(self):

Lib/typing.py

@@ -714,9 +714,9 @@ def Concatenate(self, parameters):
  raise TypeError("Cannot take a Concatenate of no types.")
  if not isinstance(parameters, tuple):
  parameters = (parameters,)
- if not isinstance(parameters[-1], ParamSpec):
+ if not (parameters[-1] is ... or isinstance(parameters[-1], ParamSpec)):
  raise TypeError("The last parameter to Concatenate should be a "
- "ParamSpec variable.")
+ "ParamSpec variable or ellipsis.")
  msg = "Concatenate[arg, ...]: each arg must be a type."
  parameters = (*(_type_check(p, msg) for p in parameters[:-1]), parameters[-1])
  return _ConcatenateGenericAlias(self, parameters,
@@ -1641,9 +1641,6 @@ def copy_with(self, params):
  return (*params[:-1], *params[-1])
  if isinstance(params[-1], _ConcatenateGenericAlias):
  params = (*params[:-1], *params[-1].__args__)
- elif not isinstance(params[-1], ParamSpec):
- raise TypeError("The last parameter to Concatenate should be a "
- "ParamSpec variable.")
  return super().copy_with(params)
 
 

Misc/NEWS.d/next/Library/2022-01-27-14-46-15.bpo-44791.tR1JFG.rst

@@ -0,0 +1 @@
+Accept ellipsis as the last argument of :data:`typing.Concatenate`.