Freeze by `unittest.mock.call??`

[chenl]

I can consistently make my Ubuntu 14.04 host freeze with this recipe:

On Python 3.6.1 installed via pyenv (https://github.com/pyenv/pyenv), and IPython 6.0.0 installed via pip run:

>>> from unittest.mock import call
>>> call??

Observe the entire host stop responding, as if all the CPU and/or memory are consumed by IPython.

[takluyver]

I cheerfully tried to reproduce this and then had to reboot my computer. That will teach me ;-)

My guess is that our introspection machinery clashes with the highly dynamic nature of mock objects. I'll look into it.

[takluyver]

Gah, it's in Python itself. inspect.getsourcelines(unittest.mock.call) is enough to trigger it. I'll file an upstream bug.

[takluyver]

In fact, there already is one: http://bugs.python.org/issue25532

[takluyver]

It's been fixed in Python now, so it should be safe from Python 3.7, 3.6.2 and 3.5.4. I don't think we can easily work around it in IPython, but I'll leave this open and if more people run into it, we can look at monkeypatching inspect.