Tracebacks are not shown right away when connecting to 'ipython kernel' from 'jupyter console'

[asmeurer]

If I start ipython kernel in one terminal and start jupyter console --existing <.json from ipython kernel> in another terminal, any command that produces an exception causes an error. The output of the exception is not shown immediately after pressing Enter. After pressing Enter a second time, it shows the exception and also an error message from the kernel

In [1]: b64decode('x')

In [1]: ---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-1-182bb76b5423> in <module>
----> 1 b64decode('x')

NameError: name 'b64decode' is not defined
/Users/aaronmeurer/anaconda3/envs/pyflyby/lib/python2.7/site-packages/jupyter_console/ptshell.py:623: UserWarning: The kernel did not respond properly to an is_complete_request: {'parent_header': {u'username': u'aaronmeurer', u'version': u'5.3', u'msg_type': u'execute_request', u'msg_id': u'8a3e61ee-b38698ab3a87e1d7244a6c46', u'session': u'2487d330-2d0fe213a7e17404d7518dfd', u'date': datetime.datetime(2019, 9, 23, 19, 47, 37, 186415, tzinfo=tzutc())}, 'msg_type': u'execute_reply', 'msg_id': u'490e53e1-b166e96a1846e72a884b65d1', 'content': {u'status': u'error', u'ename': u'NameError', u'evalue': u"name 'b64decode' is not defined", u'traceback': [u'\x1b[0;31m---------------------------------------------------------------------------\x1b[0m', u'\x1b[0;31mNameError\x1b[0m                                 Traceback (most recent call last)', u"\x1b[0;32m<ipython-input-1-182bb76b5423>\x1b[0m in \x1b[0;36m<module>\x1b[0;34m\x1b[0m\n\x1b[0;32m----> 1\x1b[0;31m \x1b[0mb64decode\x1b[0m\x1b[0;34m(\x1b[0m\x1b[0;34m'x'\x1b[0m\x1b[0;34m)\x1b[0m\x1b[0;34m\x1b[0m\x1b[0;34m\x1b[0m\x1b[0m\n\x1b[0m", u"\x1b[0;31mNameError\x1b[0m: name 'b64decode' is not defined"], u'execution_count': 1, u'user_expressions': {}, u'engine_info': {u'engine_id': -1, u'method': u'execute', u'engine_uuid': u'7ac3b0bd-8d74-4d39-b0de-e7f04676b034'}, u'payload': []}, 'header': {u'username': u'aaronmeurer', u'version': u'5.3', u'msg_type': u'execute_reply', u'msg_id': u'490e53e1-b166e96a1846e72a884b65d1', u'session': u'37ebdc70-3e2fce541a70bb4c3b93f4de', u'date': datetime.datetime(2019, 9, 23, 19, 47, 37, 401944, tzinfo=tzutc())}, 'buffers': [], 'metadata': {u'started': u'2019-09-23T19:47:37.188714Z', u'dependencies_met': True, u'status': u'error', u'engine': u'7ac3b0bd-8d74-4d39-b0de-e7f04676b034'}}.
  warn('The kernel did not respond properly to an is_complete_request: %s.' % str(msg))

If I use jupyter kernel instead of ipython kernel to start the kernel, it works fine.

Is there any reason to use ipython kernel over jupyter kernel? I noticed that jupyter kernel seems to behave better in general, so I'm wondering if ipython kernel is deprecated.

[telamonian]

I'm able to reproduce this as well, but only in a fresh virtual environment. In my main environment, I don't see the problem. There must be some recent update in some package that's to blame. It does not appear to be an issue with ipython itself (I just ran pip install -U ipython and tried again).

[telamonian]

I think I got the problem package. Doing:

pip install -U ipykernel

in my main env now allows me to reproduce the OP's issue

[asmeurer]

Yes, there's definitely a newish version of something that causes this. It didn't happen a few months ago.

[asmeurer]

Based on Travis history, this may have broken somewhere between ipykernel 5.1.1 and 5.1.2.

[asmeurer]

Yep, that is the problem. I bisected it to ipykernel commit 970ba1af5d441fbeec4e695c42eeea7eb8e6f05a, from ipython/ipykernel#412. CC @MSeal. Someone with the permissions to do so might want to move this issue to the ipykernel repo.

[asmeurer]

Actually it looks like this is already fixed in ipykernel master. Any chance we could get a release @Carreau?