With the imaplib.Debug=3 (or greater) imaplib.noop() will crash if there are any untagged responses present.

The _dump_ur() function has not been converted to expect bytes in the lambda variable x[1]. An abbreviate example of the 'dict' parameter would be:

{'READ-WRITE': [b''], 'FETCH': [b'1 (FLAGS (\\Recent NonJunk))']}

This _dump_ur() function needs converting to Python 3.x, say, change the map/lambda line to:
  l = map(lambda x:'%s: %r' % (x[0], x[1]), l)


A sample crash inducing session produced by the attached file (using another email client to produce untagged responses for NOOP):

  20:01.23 imaplib version 2.58
  20:01.23 new IMAP4 connection, tag=b'LMHB'
  20:01.48 CAPABILITIES: ('IMAP4REV1', 'LITERAL+', 'SASL-IR', 'LOGIN-REFERRALS', 'ID', 'ENABLE', 'IDLE', 'NAMESPACE', 'AUTH=PLAIN', 'AUTH=LOGIN')
Traceback (most recent call last):
  File "E:/temp/imap-idle/imaplib-noop.py", line 18, in <module>
    connection.noop()  # Crashes here.
  File "C:\Python35\lib\imaplib.py", line 656, in noop
    self._dump_ur(self.untagged_responses)
  File "C:\Python35\lib\imaplib.py", line 1210, in _dump_ur
    self._mesg('untagged responses dump:%s%s' % (t, t.join(l)))
  File "C:\Python35\lib\imaplib.py", line 1209, in <lambda>
    l = map(lambda x:'%s: "%s"' % (x[0], x[1][0] and '" "'.join(x[1]) or ''), l)
TypeError: sequence item 0: expected str instance, bytes found

I've attached a patch file of the proposed change which seems correct

Fixes syntax & line length issues in previous patch

That is a show-stopper, and the patch works fine.
Should I submit a PR with a special test-case with debug >= 3 just for this?

That sounds reasonable, if the debug output doesn't pollute the test run output.

Removing 3.5 as it is in security fix mode. Also, the PR just contains the test case that would trigger the condition and not the actual code.

Hey ankostis, 

Please let us know if you've time to complete the PR.

Thank you :)

Dear Sanyam,

My apologies, it's been almost a year that i don't need the fix for this
code,
my app has been graciously decommissioned, and i don;t have any time for it.

Best,
  Kostis

On Fri, 9 Aug 2019 at 21:35, Sanyam Khurana <report@bugs.python.org> wrote:

>
> Sanyam Khurana <sanyam.khurana01@gmail.com> added the comment:
>
> Hey ankostis,
>
> Please let us know if you've time to complete the PR.
>
> Thank you :)
>
> ----------
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue26543>
> _______________________________________
>

>
> BTW, i went back to my code and pasted what seemed to cure the problem,
>
added in commit 2b99cec  in my PR.  But i don't have much time to track if
it really works.
I hope it will help you resolve the issue.

Best,
  Kostis

New changeset 8a3d2af997e3702eac4c5b012537be39ada36888 by Sanyam Khurana in branch 'master':
bpo-26543: Fix IMAP4.noop when debug mode is enabled (GH-15206)
https://github.com/python/cpython/commit/8a3d2af997e3702eac4c5b012537be39ada36888

Merged, thanks for the fix.