[Python-checkins] bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter. (GH-27515)

serhiy-storchaka webhook-mailer at python.org
Mon Aug 2 02:18:18 EDT 2021

commit: f92b9133ef67e77605cbd315b6b6c81036ce110e
branch: main
author: Serhiy Storchaka <storchaka at gmail.com>
committer: serhiy-storchaka <storchaka at gmail.com>
date: 2021-08-02T09:17:46+03:00

bpo-44793: Fix checking the number of arguments when subscribe a generic type with ParamSpec parameter. (GH-27515)

For example Callable[P, T][[int], str, float] will now raise an error.

Use also term "arguments" instead of "parameters" in error
message for too few/many arguments.

A Misc/NEWS.d/next/Library/2021-07-31-20-28-20.bpo-44793.woaQSg.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 fbdf634c5c3be..6cd83a1586a13 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -626,8 +626,6 @@ def test_consistency(self):
         self.assertEqual(c1.__args__, c2.__args__)
         self.assertEqual(hash(c1.__args__), hash(c2.__args__))
-    test_errors = skip("known bug #44793")(BaseCallableTests.test_errors)
 class CollectionsCallableTests(BaseCallableTests, BaseTestCase):
     Callable = collections.abc.Callable
@@ -4588,6 +4586,10 @@ class X(Generic[T, P]):
         G1 = X[int, P_2]
         self.assertEqual(G1.__args__, (int, P_2))
         self.assertEqual(G1.__parameters__, (P_2,))
+        with self.assertRaisesRegex(TypeError, "few arguments for"):
+            X[int]
+        with self.assertRaisesRegex(TypeError, "many arguments for"):
+            X[int, P_2, str]
         G2 = X[int, Concatenate[int, P_2]]
         self.assertEqual(G2.__args__, (int, Concatenate[int, P_2]))
diff --git a/Lib/typing.py b/Lib/typing.py
index 702bb647269d0..16ad5ce7c2d04 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -228,7 +228,7 @@ def _check_generic(cls, parameters, elen):
         raise TypeError(f"{cls} is not a generic class")
     alen = len(parameters)
     if alen != elen:
-        raise TypeError(f"Too {'many' if alen > elen else 'few'} parameters for {cls};"
+        raise TypeError(f"Too {'many' if alen > elen else 'few'} arguments for {cls};"
                         f" actual {alen}, expected {elen}")
 def _prepare_paramspec_params(cls, params):
@@ -239,6 +239,7 @@ def _prepare_paramspec_params(cls, params):
     if len(cls.__parameters__) == 1 and len(params) > 1:
         return (params,)
+        _check_generic(cls, params, len(cls.__parameters__))
         _params = []
         # Convert lists to tuples to help other libraries cache the results.
         for p, tvar in zip(params, cls.__parameters__):
@@ -1022,10 +1023,11 @@ def __getitem__(self, params):
         if not isinstance(params, tuple):
             params = (params,)
         params = tuple(_type_convert(p) for p in params)
-        if self._paramspec_tvars:
-            if any(isinstance(t, ParamSpec) for t in self.__parameters__):
-                params = _prepare_paramspec_params(self, params)
-        _check_generic(self, params, len(self.__parameters__))
+        if (self._paramspec_tvars
+                and any(isinstance(t, ParamSpec) for t in self.__parameters__)):
+            params = _prepare_paramspec_params(self, params)
+        else:
+            _check_generic(self, params, len(self.__parameters__))
         subst = dict(zip(self.__parameters__, params))
         new_args = []
@@ -1292,7 +1294,8 @@ def __class_getitem__(cls, params):
             # Subscripting a regular Generic subclass.
             if any(isinstance(t, ParamSpec) for t in cls.__parameters__):
                 params = _prepare_paramspec_params(cls, params)
-            _check_generic(cls, params, len(cls.__parameters__))
+            else:
+                _check_generic(cls, params, len(cls.__parameters__))
         return _GenericAlias(cls, params,
                              _typevar_types=(TypeVar, ParamSpec),
diff --git a/Misc/NEWS.d/next/Library/2021-07-31-20-28-20.bpo-44793.woaQSg.rst b/Misc/NEWS.d/next/Library/2021-07-31-20-28-20.bpo-44793.woaQSg.rst
new file mode 100644
index 0000000000000..1d94d67615a47
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-07-31-20-28-20.bpo-44793.woaQSg.rst
@@ -0,0 +1,2 @@
+Fix checking the number of arguments when subscribe a generic type with
+``ParamSpec`` parameter.

More information about the Python-checkins mailing list