From 8be6c5b951c4c13eea61aabacd1ef4cbbb1a8397 Mon Sep 17 00:00:00 2001
From: Rudy Celekli <rudy@gradiahq.com>
Date: Sun, 1 Nov 2026 11:59:27 -0500
Subject: [PATCH] Fix duplicate argument checks for normalized Unicode names

---
 AUTHORS.txt                |  1 +
 parso/python/errors.py     | 15 +++++++++------
 test/test_python_errors.py | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 6 deletions(-)

diff --git a/AUTHORS.txt b/AUTHORS.txt
index 451918f..385b068 100644
--- a/AUTHORS.txt
+++ b/AUTHORS.txt
@@ -55,5 +55,6 @@ Tim Gates (@timgates42) <tim.gates@iress.com>
 Batuhan Taskaya (@isidentical) <isidentical@gmail.com>
 Jocelyn Boullier (@Kazy) <jocelyn@boullier.bzh>
 
+Rudy Celekli (@rudycelekli)
 
 Note: (@user) means a github user name.
diff --git a/parso/python/errors.py b/parso/python/errors.py
index b498af3..ba4ea9b 100644
--- a/parso/python/errors.py
+++ b/parso/python/errors.py
@@ -3,6 +3,7 @@
 import sys
 import warnings
 import re
+import unicodedata
 from contextlib import contextmanager
 
 from parso.normalizer import Normalizer, NormalizerConfig, Issue, Rule
@@ -942,14 +943,15 @@ def is_issue(self, node):
                 else:  # Is a keyword argument.
                     kw_only = True
                     if first.type == 'name':
-                        if first.value in arg_set:
+                        name = unicodedata.normalize('NFKC', first.value)
+                        if name in arg_set:
                             # f(x=1, x=2)
                             message = "keyword argument repeated"
                             if self._normalizer.version >= (3, 9):
-                                message += ": {}".format(first.value)
+                                message += ": {}".format(name)
                             self.add_issue(first, message=message)
                         else:
-                            arg_set.add(first.value)
+                            arg_set.add(name)
             else:
                 if kw_unpacking_only:
                     # f(**x, y)
@@ -978,13 +980,14 @@ def is_issue(self, node):
                     default_only = False
                 continue
 
-            if p.name.value in param_names:
+            name = unicodedata.normalize('NFKC', p.name.value)
+            if name in param_names:
                 if sys.version_info[:2] < (3, 15):
                     message = "duplicate argument '%s' in function definition"
                 else:
                     message = "duplicate parameter '%s' in function definition"
-                self.add_issue(p.name, message=message % p.name.value)
-            param_names.add(p.name.value)
+                self.add_issue(p.name, message=message % name)
+            param_names.add(name)
 
             if not star_seen:
                 if p.default is None and not p.star_count:
diff --git a/test/test_python_errors.py b/test/test_python_errors.py
index 56795f2..a453ba3 100644
--- a/test/test_python_errors.py
+++ b/test/test_python_errors.py
@@ -456,6 +456,38 @@ def test_forbidden_name(template, target):
     assert _get_error_list(template.format(target=target), version="3")
 
 
+@pytest.mark.parametrize('code', [
+    'def f(K, K): pass',
+    'def f(K, K): pass',
+    'def f(a, ａ): pass',
+    'def f(K, *, K): pass',
+    'lambda K, K: None',
+    'lambda a, ａ: None',
+    'f(K=1, K=2)',
+    'f(K=1, K=2)',
+    'f(a=1, ａ=2)',
+])
+def test_nfkc_duplicate_arguments(code):
+    wanted, line_nr = _get_actual_exception(code)
+    errors = _get_error_list(code)
+
+    error, = errors
+    assert error.message in wanted
+    assert error.start_pos[0] == line_nr
+    assert parso.parse(code).get_code() == code
+
+
+@pytest.mark.parametrize('code', [
+    'def f(K, k): pass',
+    'def f(K, K2): pass',
+    'lambda K, k: None',
+    'f(K=1, k=2)',
+])
+def test_distinct_unicode_arguments(code):
+    compile(code, '<test>', 'exec')
+    assert not _get_error_list(code)
+
+
 def test_repeated_kwarg():
     # python 3.9+ shows which argument is repeated
     assert (