pythongh-145966: Fix _csv DIALECT_GETATTR macro silently masking non-AttributeError exceptions

The DIALECT_GETATTR macro in dialect_new() unconditionally called
PyErr_Clear() when PyObject_GetAttrString() failed, which suppressed
all exceptions including MemoryError, KeyboardInterrupt, and
RuntimeError. Now only AttributeError is cleared; other exceptions
propagate via the existing error handling path.

Author: raminfp

Lib/test/test_csv.py

@@ -1281,6 +1281,20 @@ class mydialect(csv.Dialect):
                                       skipinitialspace=True)
 
 
+    def test_dialect_getattr_non_attribute_error_propagates(self):
+        # gh-145966: non-AttributeError exceptions raised by __getattr__
+        # during dialect attribute lookup must propagate, not be silenced.
+        class BadDialect:
+            def __getattr__(self, name):
+                raise RuntimeError("boom")
+
+        with self.assertRaises(RuntimeError):
+            csv.reader([], dialect=BadDialect())
+
+        with self.assertRaises(RuntimeError):
+            csv.writer(StringIO(), dialect=BadDialect())
+
+
 class TestSniffer(unittest.TestCase):
     sample1 = """\
 Harry's, Arlington Heights, IL, 2/1/03, Kimi Hayes

Misc/NEWS.d/next/Library/2026-03-15-00-00-00.gh-issue-145966.tCI0uD4I.rst

@@ -0,0 +1,4 @@
+Fixed ``DIALECT_GETATTR`` macro in :mod:`csv` to only clear
+:exc:`AttributeError` exceptions. Previously, all exceptions (including
+:exc:`MemoryError` and :exc:`KeyboardInterrupt`) were silently suppressed
+when looking up dialect attributes.

Modules/_csv.c

@@ -501,8 +501,13 @@ dialect_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
         do {                                             \
             if (v == NULL) {                             \
                 v = PyObject_GetAttrString(dialect, n);  \
-                if (v == NULL)                           \
-                    PyErr_Clear();                       \
+                if (v == NULL) {                         \
+                    if (PyErr_ExceptionMatches(           \
+                            PyExc_AttributeError))       \
+                        PyErr_Clear();                   \
+                    else                                 \
+                        goto err;                        \
+                }                                        \
             }                                            \
         } while (0)
         DIALECT_GETATTR(delimiter, "delimiter");