gh-87106: Fix inspect.signature.bind() handling of positional-only arguments with **kwargs (GH-103404)

Lib/inspect.py

@@ -3106,6 +3106,8 @@ class Signature:
         parameters_ex = ()
         arg_vals = iter(args)
 
+        pos_only_param_in_kwargs = []
+
         while True:
             # Let's iterate through the positional arguments and corresponding
             # parameters
@@ -3126,10 +3128,10 @@ class Signature:
                         break
                     elif param.name in kwargs:
                         if param.kind == _POSITIONAL_ONLY:
-                            msg = '{arg!r} parameter is positional only, ' \
+                            # Raise a TypeError once we are sure there is no
-                                  'but was passed as a keyword'
+                            # **kwargs param later.
-                            msg = msg.format(arg=param.name)
+                            pos_only_param_in_kwargs.append(param)
-                            raise TypeError(msg) from None
+                            continue
                         parameters_ex = (param,)
                         break
                     elif (param.kind == _VAR_KEYWORD or
@@ -3211,20 +3213,22 @@ class Signature:
                                     format(arg=param_name)) from None
 
             else:
-                if param.kind == _POSITIONAL_ONLY:
-                    # This should never happen in case of a properly built
-                    # Signature object (but let's have this check here
-                    # to ensure correct behaviour just in case)
-                    raise TypeError('{arg!r} parameter is positional only, '
-                                    'but was passed as a keyword'. \
-                                    format(arg=param.name))
-
                 arguments[param_name] = arg_val
 
         if kwargs:
             if kwargs_param is not None:
                 # Process our '**kwargs'-like parameter
                 arguments[kwargs_param.name] = kwargs
+            elif pos_only_param_in_kwargs:
+                raise TypeError(
+                    'got some positional-only arguments passed as '
+                    'keyword arguments: {arg!r}'.format(
+                        arg=', '.join(
+                            param.name
+                            for param in pos_only_param_in_kwargs
+                        ),
+                    ),
+                )
             else:
                 raise TypeError(
                     'got an unexpected keyword argument {arg!r}'.format(

Lib/test/test_inspect/test_inspect.py

@@ -5089,15 +5089,30 @@ class TestSignatureBind(unittest.TestCase):
         self.assertEqual(self.call(test, 1, 2, foo=4, bar=5),
                          (1, 2, 3, 4, 5, {}))
 
-        with self.assertRaisesRegex(TypeError, "but was passed as a keyword"):
+        self.assertEqual(self.call(test, 1, 2, foo=4, bar=5, c_po=10),
-            self.call(test, 1, 2, foo=4, bar=5, c_po=10)
+                         (1, 2, 3, 4, 5, {'c_po': 10}))
 
-        with self.assertRaisesRegex(TypeError, "parameter is positional only"):
+        self.assertEqual(self.call(test, 1, 2, 30, c_po=31, foo=4, bar=5),
-            self.call(test, 1, 2, c_po=4)
+                         (1, 2, 30, 4, 5, {'c_po': 31}))
 
-        with self.assertRaisesRegex(TypeError, "parameter is positional only"):
+        self.assertEqual(self.call(test, 1, 2, 30, foo=4, bar=5, c_po=31),
+                         (1, 2, 30, 4, 5, {'c_po': 31}))
+
+        self.assertEqual(self.call(test, 1, 2, c_po=4),
+                         (1, 2, 3, 42, 50, {'c_po': 4}))
+
+        with self.assertRaisesRegex(TypeError, "missing 2 required positional arguments"):
             self.call(test, a_po=1, b_po=2)
 
+        def without_var_kwargs(c_po=3, d_po=4, /):
+            return c_po, d_po
+
+        with self.assertRaisesRegex(
+            TypeError,
+            "positional-only arguments passed as keyword arguments: 'c_po, d_po'",
+        ):
+            self.call(without_var_kwargs, c_po=33, d_po=44)
+
     def test_signature_bind_with_self_arg(self):
         # Issue #17071: one of the parameters is named "self
         def test(a, self, b):

Misc/NEWS.d/next/Library/2023-04-10-00-04-37.gh-issue-87106.UyBnPQ.rst

@@ -0,0 +1,3 @@
+Fixed handling in :meth:`inspect.signature.bind` of keyword arguments having
+the same name as positional-only arguments when a variadic keyword argument
+(e.g. ``**kwargs``) is present.