bug#21421: 24.5; python mode interpreter path problem on windows.

[Currell Berry]

Hello,

python-shell-parse-command in python.el appears to have an issue on 
Windows
which prevents proper startup of the python interpreter depending on the
interpreter's path.  Here is the current version of 
python-shell-parse-command in python.el, as of Emacs 24.5.1.

 (defun python-shell-parse-command ()    ;FIXME: why name it "parse"?
   "Calculate the string used to execute the inferior Python process."
   ;; FIXME: process-environment doesn't seem to be used anywhere within
   ;; this let.
   (let ((process-environment 
(python-shell-calculate-process-environment))
         (exec-path (python-shell-calculate-exec-path)))
     (format "%s %s"
             ;; FIXME: Why executable-find?
             (shell-quote-argument
              (executable-find python-shell-interpreter))
             python-shell-interpreter-args)))

The problem is with the usage of "shell-quote-argument" to quote the 
pathname coming out of "executable-find".

Suppose you have python installed at "C:\Anaconda\python.exe", and 
"C:\Anaconda" is on your path.

Then when we run
         (executable-find python-shell-interpreter)
we get the output
        "c:/Anaconda/python.exe"
This is a valid path which can be used to launch python.

However
        (shell-quote-argument "c:/Anaconda/python.exe")
results in
        "c\\:/Anaconda/python.exe"
This is NOT a valid windows path, as an extra backquote has been
inserted before the colon (second character).

Since python-parse-interpeter uses shell-quote-argument, you get the 
following error when you run "run-python" to start up a python 
interpreter.

"apply: Searching for program: no such file or directory, 
c\:/Anaconda/python.exe"

If I modify Python.el to remove the call to "shell-quote-argument",
run-python works properly on my system.

Here is the value of my PATH in emacs.
(getenv "PATH")
":/usr/local/bin:/mingw/bin:/bin;C:\\Program 
Files\\ImageMagick-6.9.2-Q16;C:\\windows\\system32;C:\\windows;C:\\windows\\System32\\Wbem;C:\\windows\\System32\\WindowsPowerShell\\v1.0\\;C:\\Program 
Files (x86)\\Git\\cmd;C:\\Anaconda;C:\\Program Files 
(x86)\\emacs\\bin;C:\\MinGW\\bin;C:\\MinGW\\msys\\1.0;C:\\Program 
Files\\gs\\gs9.09\\lib;C:\\Program Files\\gs\\gs9.09\\bin;C:\\Program 
Files (x86)\\Calibre2\\;C:\\Program Files 
(x86)\\Graphviz2.38\\bin;C:\\Program Files (x86)\\MiKTeX 
2.9\\miktex\\bin;C:\\Users\\vancan1ty\\AppData\\Roaming\\cabal\\bin;C:\\Users\\vancan1ty\\AppData\\Roaming\\npm;C:\\Python27\\Scripts;C:\\Program 
Files (x86)\\Nmap;C:\\Program Files\\Boot2Docker for 
Windows;C:\\altera\\13.0sp1\\modelsim_ase\\win32aloem;C:\\Users\\vancan1ty\\AppData\\Local\\Pandoc\\"

In GNU Emacs 24.5.1 (i686-pc-mingw32)
 of 2015-04-11 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/usr --host=i686-pc-mingw32'

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252

Major mode: Python

Minor modes in effect:
  shell-dirtrack-mode: t
  evil-mode: t
  global-undo-tree-mode: t
  undo-tree-mode: t
  evil-local-mode: t
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
C-; is undefined
Quit [2 times]
Making completion list... [4 times]
Saving file c:/Program Files 
(x86)/emacs/share/emacs/24.5/lisp/progmodes/python.el...
Wrote c:/Program Files 
(x86)/emacs/share/emacs/24.5/lisp/progmodes/python.el
byte-code: Beginning of buffer [2 times]
Can't guess python-indent-offset, using defaults: 4
apply: Searching for program: no such file or directory, 
c\:/Anaconda/python.exe
progn: End of line [2 times]
user-error: Please specify a file name for the buffer [2 times]
byte-code: End of buffer [12 times]

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rfc822 mml mml-sec mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mail-utils python cua-base eieio-opt
speedbar sb-image ezimage dframe compile warnings skeleton derived pcase
rx loadhist ace-window avy vc-git json help-mode shell misearch
multi-isearch ob-dot org org-macro org-footnote org-pcomplete pcomplete
org-list org-faces org-entities noutline outline easy-mmode org-version
ob-emacs-lisp ob ob-tangle ob-ref ob-lob ob-table ob-exp org-src ob-keys
ob-comint comint ansi-color ob-core ob-eval org-compat org-macs
org-loaddefs format-spec find-func cal-menu calendar cal-loaddefs
cl-macs gv server evil evil-integration undo-tree diff evil-maps
evil-commands ffap url-parse auth-source eieio byte-opt bytecomp
byte-compile cl-extra cconv eieio-core gnus-util mm-util mail-prsvr
password-cache url-vars evil-command-window evil-types evil-search
evil-ex evil-macros evil-repeat evil-states evil-core advice help-fns
evil-common windmove thingatpt rect evil-digraphs evil-vars ring edmacro
kmacro cl-loaddefs cl-lib info easymenu package epg-config time-date
tooltip electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
dos-w32 ls-lisp w32-common-fns disp-table w32-win w32-vars 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
w32notify w32 multi-tty emacs)

Memory information:
((conses 8 284198 39511)
 (symbols 32 33119 0)
 (miscs 32 160 697)
 (strings 16 64392 15870)
 (string-bytes 1 1826027)
 (vectors 8 33104)
 (vector-slots 4 1301156 19920)
 (floats 8 112 474)
 (intervals 28 2003 81)
 (buffers 508 19))