bug#18819: 24.3.93; python-mode: fill-paragraph breaks comments in a way that annoys "flake8"

[Eric Hanchrow]

Some background: "flake8" (http://flake8.readthedocs.org/en/2.2.3/) is a
tool that examines a Python program, and complains about bad style.  I
use it frequently to ensure that my Python code conforms to the standard
conventions.

Anyhoo ... I noticed that filling a comment paragraph, in a way that
seems natural to me, leaves me with code that flake8 complains about.
Here's how to see what I saw:

* start `emacs -q`
* type C-x C-f /tmp/frotz.py RET
* enter the below two lines of Python code, including the
absurdly-long comment, into the python-mode buffer:
====8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<===
def yow():
    when = time.time() # hey you hey you hey you hey you hey you hey you hey you
====8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<===
* put point at the end of the second line, then type M-q, and then
save with C-x Cs

You'll see
====8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<===
def yow():
    when = time.time() # hey you hey you hey you hey you hey you hey
                       # you hey you
====8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<=======8-<===

... to be honest, that looks good to me; but (assuming you've got flake8
installed -- "pip install flake8" is the easiest way) if you then do M-x
compile RET flake8 frotz.py RET, you'll see (along with a few other
lines that aren't relevant here)

    frotz.py:3:24: E111 indentation is not a multiple of four
    frotz.py:3:24: E113 unexpected indentation

So, in a perfect world, M-q would have ... somehow ... fiddled the
indentation so that flake8 was happy.  I can't offhand think of a way to
do that that wouldn't perplex the naïve user, but there you go :-)

In GNU Emacs 24.3.93.1 (x86_64-apple-darwin13.4.0, NS apple-appkit-1265.21)
 of 2014-10-06 on Eric-Hanchrows-iMac.local
Repository revision: eliz@gnu.org-20140929191028-lti2lybtzzrnjppc
Windowing system distributor `Apple', version 10.3.1343
Configured using:
 `configure --with-ns'

Important settings:
  locale-coding-system: utf-8-unix

Major mode: Python

Minor modes in effect:
  shell-dirtrack-mode: t
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
C-x C-f / t m p / f r o t z . p y C-j C-y C-p C-p C-p
C-p C-o d e f SPC y o w M-( C-e : C-M-p M-\ C-n <tab>
C-n C-n C-n M-m C-SPC C-p C-p C-f C-f C-x r d C-n C-n
M-^ M-^ M-^ M-; M-> C-x C-s C-p C-p C-e M-q C-x C-s
M-x c o m p i l e <return> C-a C-k f l a k e 8 7 <backspace>
SPC f r <tab> <return> M-x c o l u m n <tab> <return>
M-m C-h c M-q C-d C-p C-d C-n M-^ M-^ M-> C-p C-p M-f
M-f M-f M-f M-b C-k h e y SPC y o u SPC M-b M-b C-k
C-y C-y C-y C-y C-y C-y C-y C-x C-s M-q C-x C-s C-x
o g C-x o M-m C-d M-^ C-x C-s M-x r e p o e <backspace>
r t - e m <tab> <return>

Recent messages:
M-q runs the command fill-paragraph
Mark set [8 times]
Saving file /tmp/frotz.py...
Wrote /tmp/frotz.py
Saving file /tmp/frotz.py...
Wrote /tmp/frotz.py
(No files need saving)
Compilation exited abnormally with code 1
Saving file /tmp/frotz.py...
Wrote /tmp/frotz.py

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
help-fns mail-prsvr mail-utils cus-start cus-load shell pcomplete
compile rect python easymenu json comint ring cl-loaddefs cl-lib
ansi-color time-date tooltip electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel ns-win tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment lisp-mode prog-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer nadvice
loaddefs button faces cus-face macroexp files text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process cocoa ns
multi-tty emacs)

Memory information:
((conses 16 109477 8810)
 (symbols 48 28490 0)
 (miscs 40 62 307)
 (strings 32 32817 4135)
 (string-bytes 1 594338)
 (vectors 16 11023)
 (vector-slots 8 401785 5355)
 (floats 8 62 391)
 (intervals 56 330 8)
 (buffers 960 13))