Address review comments

Lib/email/_policybase.py

@@ -15,12 +15,14 @@
     'compat32',
     ]
 
+# equivalent to pattern re.compile("[!-9;-~]+$")
 valid_header_name_re = re.compile("[\041-\071\073-\176]+$")
 
 def validate_header_name(name):
     # Validate header name according to RFC 5322
     if not valid_header_name_re.match(name):
-        raise ValueError(f"Header field name contains invalid characters: {name!r}")
+        raise ValueError(
+            f"Header field name contains invalid characters: {name!r}")
 
 class _PolicyBase:
 

Lib/test/test_email/test_message.py

@@ -1024,11 +1024,14 @@ def test_invalid_header_names(self):
                             policy=thispolicy.__class__.__name__,
                             method=method,
                             ):
-                        with self.assertRaises(ValueError) as cm:
-                            getattr(EmailMessage(policy=thispolicy), method)(name, value)
-                        msg = str(cm.exception)
-                        self.assertRegex( msg, '(?i)(?=.*invalid)(?=.*header)(?=.*name)')
-                        self.assertIn(f"{name!r}", msg)
+                        message = EmailMessage(policy=thispolicy)
+                        method = getattr(message, method)
+                        with self.assertRaisesRegex(
+                            ValueError,
+                            '(?i)(?=.*invalid)(?=.*header)(?=.*name)'
+                            ) as cm:
+                            method(name,value)
+                        self.assertIn(f"{name!r}", str(cm.exception))
 
     def test_get_body_malformed(self):
         """test for bpo-42892"""