"Fix" Py2 error formatting issue

2 files changed, 17 insertions, 4 deletions

diff --git a/Cython/Utility/MatchCase.c b/Cython/Utility/MatchCase.c
index 3f71ed1e8..08eb50433 100644
--- a/Cython/Utility/MatchCase.c
+++ b/Cython/Utility/MatchCase.c
@@ -503,8 +503,15 @@ static int __Pyx_MatchCase_CheckDuplicateKeys(PyObject *keys[], Py_ssize_t nFixe
     return 0;
 
     raise_error:
+    #if PY_MAJOR_VERSION > 2
     PyErr_Format(PyExc_ValueError,
                  "mapping pattern checks duplicate key (%R)", key);
+    #else
+    // DW really can't be bothered working around features that don't exist in
+    // Python 2, so just provide less information!
+    PyErr_SetString(PyExc_ValueError,
+                    "mapping pattern checks duplicate key");
+    #endif
     bad:
     Py_DECREF(var_keys_set);
     return -1;
diff --git a/tests/run/extra_patma_py.py b/tests/run/extra_patma_py.py
index 0ff51e25a..182529683 100644
--- a/tests/run/extra_patma_py.py
+++ b/tests/run/extra_patma_py.py
@@ -2,6 +2,7 @@
 # tag: pure3.10
 
 import array
+import sys
 
 def test_array_is_sequence(x):
     """
@@ -27,10 +28,15 @@ def test_duplicate_keys(key1, key2):
 
     >>> test_duplicate_keys("a", "b")
     True
-    >>> test_duplicate_keys("a", "a")
-    Traceback (most recent call last):
-    ...
-    ValueError: mapping pattern checks duplicate key ('a')
+
+    Slightly awkward doctest to work around Py2 incompatibility
+    >>> try:
+    ...    test_duplicate_keys("a", "a")
+    ... except ValueError as e:
+    ...    if sys.version_info[0] > 2:
+    ...        assert e.args[0] == "mapping pattern checks duplicate key ('a')", e.args[0]
+    ...    else:
+    ...        assert e.args[0] == "mapping pattern checks duplicate key"
     """
     class Keys:
         KEY_1 = key1