Seqfault in on_trait_change about traitlets

[jenshnielsen]

BTW the Matplotlib build log is in https://travis-ci.org/matplotlib/matplotlib/jobs/103175772

[jenshnielsen]

Looking over Matplotlib log we only seem to see it with python 3 (Specifically python 3.5) On the branches where the docs are build with python 2.7 this doesn't happen.

[jenshnielsen]

Im also seeing it in a fresh conda environment

In [1]:
Do you really want to exit ([y]/n)? y
Fatal Python error: PyImport_GetModuleDict: no module dictionary!

Current thread 0x00007fff7844b000 (most recent call first):
  File "/Users/jhn/miniconda3/lib/python3.5/site-packages/traitlets/traitlets.py", line 1136 in on_trait_change
  File "/Users/jhn/miniconda3/lib/python3.5/site-packages/IPython/core/extensions.py", line 64 in __del__
/Users/jhn/miniconda3/bin/python.app: line 3:  4033 Abort trap: 6           /Users/jhn/miniconda3/python.app/Contents/MacOS/python "$@"

[minrk]

I can see this, too sometimes. Seems like it has to be a bug in Python 3.5, even if it's triggered by a change in traitlets. I'll try to see if I can figure out what caused it.

[jenshnielsen]

@minrk Thanks, It sounds plausible that it's a bug in Python 3.5

[minrk]

I just need to narrow it down to what's the exact cause. I've seen it, but I cannot reproduce it reliably, which makes it harder to find what is the relevant change. I can only reproduce the error about 1% of the time, which suggests to me that it might be threading related.

[minrk]

I think I found it: the cause appears to be the deprecation warning that we throw, since on_trait_change is deprecated. I'm guessing it's the inspection used to show the warning message that's failing.

Unfortunately, I don't know a way to fix this in traitlets, since it seems like the only thing we are doing is a simple warning.

Fortunately, though, the __del__ call here that's the direct cause is unnecessary and already removed in master (ipython/ipython#9040). My proposal is to backport this fix and immediately release IPython 4.0.3, while we work with CPython to figure out the upstream bug.

[jenshnielsen]

@minrk Sounds good to me

[minrk]

Released IPython 4.0.3 with the patch. Hopefully that should tide us over while we work out what's up with Python 3.5.

[jenshnielsen]

@minrk Thanks, I will upgrade and see what happens.