[Python-modules-team] Bug#879876: ipython fails after printing help on a variable definition

[Reverend Homer]

Package: ipython
Version: 5.1.0-3
Severity: normal

Dear Maintainer,

   * What led up to the situation?

Nothing unusual, just "apt install python-ipython ipython"

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

In [1]: s = isinstance?

   * What was the outcome of this action?

In [1]: s = isinstance?
Docstring:
isinstance(object, class-or-type-or-tuple) -> bool

Return whether an object is an instance of a class or of a subclass thereof.
With a type as second argument, return whether that is the object's type.
The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
isinstance(x, A) or isinstance(x, B) or ... (etc.).
Type:      builtin_function_or_method

In [2]: s = isinstance?
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/traitlets/config/application.py", line 658, in launch_instance
    app.start()
  File "/usr/lib/python2.7/dist-packages/IPython/terminal/ipapp.py", line 348, in start
    self.shell.mainloop()
  File "/usr/lib/python2.7/dist-packages/IPython/terminal/interactiveshell.py", line 440, in mainloop
    self.interact()
  File "/usr/lib/python2.7/dist-packages/IPython/terminal/interactiveshell.py", line 423, in interact
    code = self.prompt_for_code()
  File "/usr/lib/python2.7/dist-packages/IPython/terminal/interactiveshell.py", line 333, in prompt_for_code
    pre_run=self.pre_prompt, reset_current_buffer=True)
  File "/usr/lib/python2.7/dist-packages/prompt_toolkit/interface.py", line 408, in run
    self._pre_run(pre_run)
  File "/usr/lib/python2.7/dist-packages/prompt_toolkit/interface.py", line 383, in _pre_run
    pre_run()
  File "/usr/lib/python2.7/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/python2.7/dist-packages/prompt_toolkit/buffer.py", line 372, in text
    assert self.cursor_position <= len(value)
AssertionError

If you suspect this is an IPython bug, please report it at:
    https://github.com/ipython/ipython/issues
or send an email to the mailing list at ipython-dev at scipy.org

You can print a more detailed traceback right now with "%tb", or use "%debug"
to interactively debug it.

Extra-detailed tracebacks for bug-reporting purposes can be enabled via:
    %config Application.verbose_crash=True



   * What outcome did you expect instead?

ipython prints help, removes "?" from the repl and works fine


-- System Information:
Debian Release: buster/sid
  APT prefers testing
  APT policy: (900, 'testing'), (500, 'testing-debug'), (500, 'unstable')
Architecture: amd64 (x86_64)

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

Versions of packages ipython depends on:
ii  python-ipython  5.1.0-3

ipython recommends no packages.

ipython suggests no packages.

-- no debconf information