Python completion when using pdb (M-x pdb)

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hello Emacs!

I've recently discovered that Emacs provides it's own completion
mechanism, for example when running M-x run-python. This works even with
the vanilla Python interpreter, which doesn't provide such completion
out-of-the-box itself, which is nice!

However, I couldn't make completion work in pdb. My understanding, when
searching on the web, is that it *should* work in pdb too. For example,
the commit a92066b (python.el: Fix completion for pdb interactions) made
two years ago would suggest that it should work.

Things I've tried:

1. Using M-x pdb: The buffer is not even set up for completion with
python.el. C-h k <TAB> reveals that it simply calls
`indent-for-tab-command'.

2. Once debugging, I used 'M-x run-python'. The Python process "inherited"
the already running pdb process and I could see the (Pdb) prompt from
there. (The same could have been attained by M-x run-python at first,
then execfile some/file (python 2) in wich "import pdb; pdb.set_trace()"
is used.

This time, C-h k <TAB> revealed it was bound to
`python-shell-completion-complete-or-indent', which is better. However,
attempting to tab-complete any symbol at the pdb prompt returned 'No
match' at the minibuffer.

I also tested with realgud instead of gud, with the same result.

Any pointers would be very appreciated :)

Maxim