Reject non-finite decimal.Decimal query parameters (NaN, sNaN, ±Infinity) (#1237)

Copilot · web-flow · commit c532b8d9d515 · 2026-05-15T21:06:57.000+09:00
PyMySQL already rejects non-finite `float` parameters before sending
SQL, but equivalent `decimal.Decimal` values were still serialized and
sent. This change aligns Decimal behavior with existing float safeguards
for unsupported non-finite numeric parameters.
diff --git a/pymysql/converters.py b/pymysql/converters.py
@@ -135,6 +135,8 @@ def escape_struct_time(obj, mapping=None):
 
 
 def Decimal2Literal(o, d):
+    if not o.is_finite():
+        raise ProgrammingError("%s can not be used with MySQL" % str(o).lower())
     return format(o, "f")
 
 
diff --git a/pymysql/tests/test_converters.py b/pymysql/tests/test_converters.py
@@ -1,6 +1,8 @@
 import datetime
+from decimal import Decimal
 from unittest import TestCase
 from pymysql import converters
+from pymysql.err import ProgrammingError
 
 
 __all__ = ["TestConverter"]
@@ -52,3 +54,16 @@ def test_convert_time_with_fsp(self):
         expected = datetime.time(23, 6, 20, 511581)
         time_obj = converters.convert_time("23:06:20.511581")
         self.assertEqual(time_obj, expected)
+
+    def test_decimal_special_values(self):
+        values = (
+            Decimal("NaN"),
+            Decimal("sNaN"),
+            Decimal("Infinity"),
+            Decimal("-Infinity"),
+        )
+        for value in values:
+            with self.assertRaisesRegex(
+                ProgrammingError, f"{str(value).lower()} can not be used with MySQL"
+            ):
+                converters.Decimal2Literal(value, None)
