bpo-43564: preserve original exception in args of FTP URLError (#24938)

* bpo-43564: preserve original error in args of FTP URLError

* Add NEWS blurb

Co-authored-by: Carl Meyer <[email protected]>

Author: carljm

Lib/urllib/request.py

@@ -1582,7 +1582,7 @@ def ftp_open(self, req):
             headers = email.message_from_string(headers)
             return addinfourl(fp, headers, req.full_url)
         except ftplib.all_errors as exp:
-            raise URLError(f'ftp error: {exp}') from exp
+            raise URLError(exp) from exp
 
     def connect_ftp(self, user, passwd, host, port, dirs, timeout):
         return ftpwrapper(user, passwd, host, port, dirs, timeout,

Misc/NEWS.d/next/Library/2022-10-09-12-12-38.gh-issue-87730.ClgP3f.rst

@@ -0,0 +1,3 @@
+Wrap network errors consistently in urllib FTP support, so the test suite
+doesn't fail when a network is available but the public internet is not
+reachable.