bug#23616: 25.0.94; TAB in inferior-python-mode

[Stephen Berman <stephen.berman@gmx.net>]

Doing the following (in either emacs-25 or master):

0. emacs -Q
1. M-x run-python
2. at the Python prompt type `for i in range(10):' then `RET', `TAB',
   `print i,', `RET'

results in this Python error:

IndentationError: expected an indented block

although the TAB in step 2 above visibly indents the line `print i,'.
If instead of `TAB' I type `SPC SPC SPC SPC' then after the final RET
the output is as expected:

0 1 2 3 4 5 6 7 8 9

It's not clear to me whether the above error indicates a bug in
python.el; is there some setting I haven't found that makes TAB work in
inferior-python-mode?  (In case it matter, this is with python 2.7.8., I
haven't tried with python3.)  I note that the definition of python-mode
has this line:

(set (make-local-variable 'indent-tabs-mode) nil)

which the definition of inferior-python-mode lacks; adding that line to
latter does make TAB work as I expect.  But I'm not sure whether this
setting is missing on purpose (but if so, why?).


In GNU Emacs 25.0.94.1 (x86_64-suse-linux-gnu, GTK+ Version 3.14.15)
 of 2016-05-18 built on rosalinde
Repository revision: 3b5e38cde194c4faa3865aa437b4a2749946c24d
Windowing system distributor 'The X.Org Foundation', version 11.0.11601000
System Description:	openSUSE 13.2 (Harlequin) (x86_64)

Configured using:
 'configure --with-xwidgets 'CFLAGS=-Og -g3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GCONF GSETTINGS NOTIFY
GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11 XWIDGETS

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix