bpo-35634: Raise an error when first passed kwargs contains duplicated keys. (GH-11438)

1 files changed, 46 insertions, 0 deletions

diff --git a/Lib/test/test_extcall.py b/Lib/test/test_extcall.py
index 2c1848337b..a3ff4413ee 100644
--- a/Lib/test/test_extcall.py
+++ b/Lib/test/test_extcall.py
@@ -316,6 +316,52 @@ not function
       ...
     TypeError: dir() got multiple values for keyword argument 'b'
 
+Test a kwargs mapping with duplicated keys.
+
+    >>> from collections.abc import Mapping
+    >>> class MultiDict(Mapping):
+    ...     def __init__(self, items):
+    ...         self._items = items
+    ...
+    ...     def __iter__(self):
+    ...         return (k for k, v in self._items)
+    ...
+    ...     def __getitem__(self, key):
+    ...         for k, v in self._items:
+    ...             if k == key:
+    ...                 return v
+    ...         raise KeyError(key)
+    ...
+    ...     def __len__(self):
+    ...         return len(self._items)
+    ...
+    ...     def keys(self):
+    ...         return [k for k, v in self._items]
+    ...
+    ...     def values(self):
+    ...         return [v for k, v in self._items]
+    ...
+    ...     def items(self):
+    ...         return [(k, v) for k, v in self._items]
+    ...
+    >>> g(**MultiDict([('x', 1), ('y', 2)]))
+    1 () {'y': 2}
+
+    >>> g(**MultiDict([('x', 1), ('x', 2)]))
+    Traceback (most recent call last):
+      ...
+    TypeError: g() got multiple values for keyword argument 'x'
+
+    >>> g(a=3, **MultiDict([('x', 1), ('x', 2)]))
+    Traceback (most recent call last):
+      ...
+    TypeError: g() got multiple values for keyword argument 'x'
+
+    >>> g(**MultiDict([('a', 3)]), **MultiDict([('x', 1), ('x', 2)]))
+    Traceback (most recent call last):
+      ...
+    TypeError: g() got multiple values for keyword argument 'x'
+
 Another helper function
 
     >>> def f2(*a, **b):