Apply suggestions from code review

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: sethmlarson

Lib/test/test_wsgiref.py

@@ -509,7 +509,7 @@ def testRaisesControlCharacters(self):
                 headers = Headers()
                 self.assertRaises(ValueError, headers.__setitem__, f"key{c0}", "val")
                 self.assertRaises(ValueError, headers.add_header, f"key{c0}", "val", param="param")
-                # HTAB is allowed in values, not names.
+                # HTAB (\x09) is allowed in values, not names.
                 if c0 == "\t":
                     headers["key"] = f"val{c0}"
                     headers.add_header("key", f"val{c0}")

Lib/wsgiref/headers.py

@@ -43,10 +43,11 @@ def __init__(self, headers=None):
                 self._convert_string_type(k, name=True)
                 self._convert_string_type(v)
 
-    def _convert_string_type(self, value, *, name=False):
+    def _convert_string_type(self, value, *, name):
         """Convert/check value type."""
         if type(value) is str:
-            if (_name_disallowed_re if name else _value_disallowed_re).search(value):
+            regex = (_name_disallowed_re if name else _value_disallowed_re)
+            if regex.search(value):
                 raise ValueError("Control characters not allowed in headers")
             return value
         raise AssertionError("Header names/values must be"