bpo-31507 Add docstring to parseaddr function in email.utils.parseaddr (GH-3647) (GH-3733)

(cherry picked from commit 9e7b9b21)

Lib/email/utils.py

@@ -215,6 +215,12 @@ def parsedate_to_datetime(data):
 
 
 def parseaddr(addr):
+    """
+    Parse addr into its constituent realname and email address parts.
+    
+    Return a tuple of realname and email address, unless the parse fails, in
+    which case return a 2-tuple of ('', '').
+    """
     addrs = _AddressList(addr).addresslist
     if not addrs:
         return '', ''