[Python-checkins] gh-96385: Correctly raise error on `[*T, *V]` substitution (GH-96386)

[serhiy-storchaka]

https://github.com/python/cpython/commit/75177358a62afeabd1d3aa0e9f395c2b9d4495ca
commit: 75177358a62afeabd1d3aa0e9f395c2b9d4495ca
branch: main
author: Nikita Sobolev <mail at sobolevn.me>
committer: serhiy-storchaka <storchaka at gmail.com>
date: 2022-08-30T10:34:55+03:00
summary:

gh-96385: Correctly raise error on `[*T, *V]` substitution (GH-96386)

files:
A Misc/NEWS.d/next/Library/2022-08-29-15-28-39.gh-issue-96385.uLRTsf.rst
M Lib/test/test_typing.py
M Lib/typing.py

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index ca7bd8e083c4..7eea01909ec8 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -596,6 +596,7 @@ class GenericAliasSubstitutionTests(BaseTestCase):
     def test_one_parameter(self):
         T = TypeVar('T')
         Ts = TypeVarTuple('Ts')
+        Ts2 = TypeVarTuple('Ts2')
 
         class C(Generic[T]): pass
 
@@ -621,6 +622,8 @@ class C(Generic[T]): pass
             # Should definitely raise TypeError: list only takes one argument.
             ('list[T, *tuple_type[int, ...]]',    '[int]',                   'list[int, *tuple_type[int, ...]]'),
             ('List[T, *tuple_type[int, ...]]',    '[int]',                   'TypeError'),
+            # Should raise, because more than one `TypeVarTuple` is not supported.
+            ('generic[*Ts, *Ts2]',                '[int]',                   'TypeError'),
         ]
 
         for alias_template, args_template, expected_template in tests:
diff --git a/Lib/typing.py b/Lib/typing.py
index 43ef07e50cfe..596744ed1322 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1074,7 +1074,7 @@ def __typing_subst__(self, arg):
     def __typing_prepare_subst__(self, alias, args):
         params = alias.__parameters__
         typevartuple_index = params.index(self)
-        for param in enumerate(params[typevartuple_index + 1:]):
+        for param in params[typevartuple_index + 1:]:
             if isinstance(param, TypeVarTuple):
                 raise TypeError(f"More than one TypeVarTuple parameter in {alias}")
 
diff --git a/Misc/NEWS.d/next/Library/2022-08-29-15-28-39.gh-issue-96385.uLRTsf.rst b/Misc/NEWS.d/next/Library/2022-08-29-15-28-39.gh-issue-96385.uLRTsf.rst
new file mode 100644
index 000000000000..57354826f349
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-08-29-15-28-39.gh-issue-96385.uLRTsf.rst
@@ -0,0 +1,3 @@
+Fix ``TypeVarTuple.__typing_prepare_subst__``. ``TypeError`` was not raised
+when using more than one ``TypeVarTuple``, like ``[*T, *V]`` in type alias
+substitutions.