pythongh-87106: Fix inspect.signature.bind handling of positional-only arguments with **kwargs

Author: jacobtylerwalls

Lib/inspect.py

@@ -3109,6 +3109,8 @@ def _bind(self, args, kwargs, *, partial=False):
         parameters_ex = ()
         arg_vals = iter(args)
 
+        pos_only_param_in_kwargs = []
+
         while True:
             # Let's iterate through the positional arguments and corresponding
             # parameters
@@ -3129,10 +3131,9 @@ def _bind(self, args, kwargs, *, partial=False):
                         break
                     elif param.name in kwargs:
                         if param.kind == _POSITIONAL_ONLY:
-                            msg = '{arg!r} parameter is positional only, ' \
-                                  'but was passed as a keyword'
-                            msg = msg.format(arg=param.name)
-                            raise TypeError(msg) from None
+                            # Raise a TypeError once we are sure there is no
+                            # **kwargs param later.
+                            pos_only_param_in_kwargs.append(param)
                         parameters_ex = (param,)
                         break
                     elif (param.kind == _VAR_KEYWORD or
@@ -3215,20 +3216,21 @@ def _bind(self, args, kwargs, *, partial=False):
 
             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
+                    # Restore the param in case there is a kwargs_param
+                    kwargs[param_name] = arg_val
+                else:
+                    arguments[param_name] = arg_val
 
         if kwargs:
             if kwargs_param is not None:
                 # Process our '**kwargs'-like parameter
                 arguments[kwargs_param.name] = kwargs
             else:
+                if 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)))
                 raise TypeError(
                     'got an unexpected keyword argument {arg!r}'.format(
                         arg=next(iter(kwargs))))

Lib/test/test_inspect.py

@@ -4155,18 +4155,9 @@ def test(a, *args, b, z=100, **kwargs):
         self.assertEqual(ba.args, (10, 20))
 
     def test_signature_bind_positional_only(self):
-        P = inspect.Parameter
-
-        def test(a_po, b_po, c_po=3, foo=42, *, bar=50, **kwargs):
+        def test(a_po, b_po, c_po=3, /, foo=42, *, bar=50, **kwargs):
             return a_po, b_po, c_po, foo, bar, kwargs
 
-        sig = inspect.signature(test)
-        new_params = collections.OrderedDict(tuple(sig.parameters.items()))
-        for name in ('a_po', 'b_po', 'c_po'):
-            new_params[name] = new_params[name].replace(kind=P.POSITIONAL_ONLY)
-        new_sig = sig.replace(parameters=new_params.values())
-        test.__signature__ = new_sig
-
         self.assertEqual(self.call(test, 1, 2, 4, 5, bar=6),
                          (1, 2, 4, 5, 6, {}))
 
@@ -4176,15 +4167,21 @@ def test(a_po, b_po, c_po=3, foo=42, *, bar=50, **kwargs):
         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.call(test, 1, 2, foo=4, bar=5, c_po=10)
+        self.assertEqual(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.call(test, 1, 2, c_po=4)
+        self.assertEqual(self.call(test, 1, 2, c_po=4),
+                         (1, 2, 3, 42, 50, {'c_po': 4}))
 
-        with self.assertRaisesRegex(TypeError, "parameter is positional only"):
+        with self.assertRaisesRegex(TypeError, "missing 2 required positional arguments"):
             self.call(test, a_po=1, b_po=2)
 
+        def test_without_var_kwargs(a_po, b_po, c_po=3, /, foo=42, *, bar=50):
+            return a_po, b_po, c_po, foo, bar
+
+        with self.assertRaisesRegex(TypeError, "positional-only arguments passed as keyword"):
+            self.call(test_without_var_kwargs, 1, 2, foo=4, bar=5, c_po=10)
+
     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.