[Python-modules-team] Bug#879159: ipython3: Using ? to get a docstring sometimes causes an AssertionError

[Diane Trout]

Package: ipython3
Version: 5.1.0-3
Severity: normal

Dear Maintainer,

I was trying to understand a module and when I hit a ? ipython3 exited
with the traceback below.

I looked at
https://github.com/ipython/ipython/issues/10381

And have a quick reproducer.

import numpy
x = numpy.z<TAB>
(Autocomplete to zero, add ?, hit enter)
x = numpy.zero?
(read help)
Crash


My traceback
------------
In [41]: e[0].get_properties?
Object `get_properties` not found.

In [42]: e[0].get_properties?                                                   
Traceback (most recent call last):
  File "/home/diane/.local/bin/ipython3", line 11, in <module>
    sys.exit(start_ipython())
  File "/usr/lib/python3/dist-packages/IPython/__init__.py", line 119, in start_ipython
    return launch_new_instance(argv=argv, **kwargs)
  File "/usr/lib/python3/dist-packages/traitlets/config/application.py", line 658, in launch_instance
    app.start()
  File "/usr/lib/python3/dist-packages/IPython/terminal/ipapp.py", line 348, in start
    self.shell.mainloop()
  File "/usr/lib/python3/dist-packages/IPython/terminal/interactiveshell.py", line 440, in mainloop
    self.interact()
  File "/usr/lib/python3/dist-packages/IPython/terminal/interactiveshell.py", line 423, in interact
    code = self.prompt_for_code()
  File "/usr/lib/python3/dist-packages/IPython/terminal/interactiveshell.py", line 333, in prompt_for_code
    pre_run=self.pre_prompt, reset_current_buffer=True)
  File "/usr/lib/python3/dist-packages/prompt_toolkit/interface.py", line 408, in run
    self._pre_run(pre_run)
  File "/usr/lib/python3/dist-packages/prompt_toolkit/interface.py", line 383, in _pre_run
    pre_run()
  File "/usr/lib/python3/dist-packages/IPython/terminal/interactiveshell.py", line 410, in pre_prompt
    self.pt_cli.application.buffer.text = cast_unicode_py2(self.rl_next_input)
  File "/usr/lib/python3/dist-packages/prompt_toolkit/buffer.py", line 372, in text
    assert self.cursor_position <= len(value)
AssertionError


-- System Information:
Debian Release: buster/sid
  APT prefers testing-debug
  APT policy: (500, 'testing-debug'), (500, 'stable-debug'), (500, 'testing'), (500, 'stable'), (110, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.13.0-1-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages ipython3 depends on:
ii  python3-ipython  5.1.0-3

ipython3 recommends no packages.

ipython3 suggests no packages.

-- no debconf information