bpo-44791: Fix substitution of ParamSpec in Concatenate with differen…

…t parameter expressions (GH-27518)

* Substitution with a list of types returns now a tuple of types.
* Substitution with Concatenate returns now a Concatenate with
  concatenated lists of arguments.
* Substitution with Ellipsis is not supported.
(cherry picked from commit ecfacc3)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/_collections_abc.py

@@ -500,7 +500,10 @@ def __getitem__(self, item):
  if subparams:
  subargs = tuple(subst[x] for x in subparams)
  arg = arg[subargs]
- new_args.append(arg)
+ if isinstance(arg, tuple):
+ new_args.extend(arg)
+ else:
+ new_args.append(arg)
 
  # args[0] occurs due to things like Z[[int, str, bool]] from PEP 612
  if not isinstance(new_args[0], list):

Lib/test/test_typing.py

@@ -621,10 +621,31 @@ def test_paramspec(self):
  def test_concatenate(self):
  Callable = self.Callable
  fullname = f"{Callable.__module__}.Callable"
+ T = TypeVar('T')
  P = ParamSpec('P')
- C1 = Callable[typing.Concatenate[int, P], int]
- self.assertEqual(repr(C1),
- f"{fullname}[typing.Concatenate[int, ~P], int]")
+ P2 = ParamSpec('P2')
+ C = Callable[Concatenate[int, P], T]
+ self.assertEqual(repr(C),
+ f"{fullname}[typing.Concatenate[int, ~P], ~T]")
+ self.assertEqual(C[P2, int], Callable[Concatenate[int, P2], int])
+ self.assertEqual(C[[str, float], int], Callable[[int, str, float], int])
+ 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]
+
+ C = Callable[Concatenate[int, P], int]
+ self.assertEqual(repr(C),
+ f"{fullname}[typing.Concatenate[int, ~P], int]")
+ self.assertEqual(C[P2], Callable[Concatenate[int, P2], int])
+ self.assertEqual(C[[str, float]], Callable[[int, str, float], int])
+ self.assertEqual(C[str, float], Callable[[int, str, float], int])
+ self.assertEqual(C[[]], Callable[[int], int])
+ self.assertEqual(C[Concatenate[str, P2]],
+ Callable[Concatenate[int, str, P2], int])
+ with self.assertRaises(TypeError):
+ C[...]
 
  def test_errors(self):
  Callable = self.Callable
@@ -4894,6 +4915,27 @@ def test_valid_uses(self):
  self.assertEqual(C4.__args__, (Concatenate[int, T, P], T))
  self.assertEqual(C4.__parameters__, (T, P))
 
+ def test_var_substitution(self):
+ T = TypeVar('T')
+ P = ParamSpec('P')
+ P2 = ParamSpec('P2')
+ C = Concatenate[T, P]
+ self.assertEqual(C[int, P2], Concatenate[int, P2])
+ self.assertEqual(C[int, [str, float]], (int, str, float))
+ self.assertEqual(C[int, []], (int,))
+ self.assertEqual(C[int, Concatenate[str, P2]],
+ Concatenate[int, str, P2])
+ with self.assertRaises(TypeError):
+ C[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[...]
 
 class TypeGuardTests(BaseTestCase):
  def test_basics(self):

Lib/typing.py

@@ -598,7 +598,7 @@ def Concatenate(self, parameters):
  raise TypeError("The last parameter to Concatenate should be a "
  "ParamSpec variable.")
  msg = "Concatenate[arg, ...]: each arg must be a type."
- parameters = tuple(_type_check(p, msg) for p in parameters)
+ parameters = (*(_type_check(p, msg) for p in parameters[:-1]), parameters[-1])
  return _ConcatenateGenericAlias(self, parameters)
 
 
@@ -1274,6 +1274,16 @@ def __init__(self, *args, **kwargs):
  _typevar_types=(TypeVar, ParamSpec),
  _paramspec_tvars=True)
 
+ def copy_with(self, params):
+ if isinstance(params[-1], (list, tuple)):
+ 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)
+
 
 class Generic:
  """Abstract base class for generic types.

Misc/NEWS.d/next/Library/2021-07-31-23-18-50.bpo-44791.4jFdpO.rst

@@ -0,0 +1,5 @@
+Fix substitution of :class:`~typing.ParamSpec` in
+:data:`~typing.Concatenate` with different parameter expressions.
+Substitution with a list of types returns now a tuple of types. Substitution
+with ``Concatenate`` returns now a ``Concatenate`` with concatenated lists
+of arguments.