bpo-31243: Fixed PyArg_ParseTuple failure checks. (#3171)

Lib/test/test_io.py

@@ -3253,6 +3253,26 @@ class TextIOWrapperTest(unittest.TestCase):
         t = _make_illegal_wrapper()
         self.assertRaises(TypeError, t.read)
 
+        # Issue 31243: calling read() while the return value of decoder's
+        # getstate() is invalid should neither crash the interpreter nor
+        # raise a SystemError.
+        def _make_very_illegal_wrapper(getstate_ret_val):
+            class BadDecoder:
+                def getstate(self):
+                    return getstate_ret_val
+            def _get_bad_decoder(dummy):
+                return BadDecoder()
+            quopri = codecs.lookup("quopri")
+            with support.swap_attr(quopri, 'incrementaldecoder',
+                                   _get_bad_decoder):
+                return _make_illegal_wrapper()
+        t = _make_very_illegal_wrapper(42)
+        self.assertRaises(TypeError, t.read, 42)
+        t = _make_very_illegal_wrapper(())
+        self.assertRaises(TypeError, t.read, 42)
+        t = _make_very_illegal_wrapper((1, 2))
+        self.assertRaises(TypeError, t.read, 42)
+
     def _check_create_at_shutdown(self, **kwargs):
         # Issue #20037: creating a TextIOWrapper at shutdown
         # shouldn't crash the interpreter.