gh-159739: Avoid quadratic grouped-address parsing (#159990)

Author: jelle-openai

Lib/email/_parseaddr.py

@@ -307,7 +307,7 @@ def getaddress(self):
                 if self.pos < fieldlen and self.field[self.pos] == ';':
                     self.pos += 1
                     break
-                returnlist = returnlist + self.getaddress()
+                returnlist.extend(self.getaddress())
 
         elif self.field[self.pos] == '<':
             # Address is a phrase then a route addr

Misc/NEWS.d/next/Library/2026-10-20-00-00-00.gh-issue-159739.35942a.rst

@@ -0,0 +1 @@
+Improve performance when parsing email address groups with many members.