bug#21118: 25.0.50; Comint delete behaving differently for Python vs Scheme

[Nishant Varma]

I compiled Emacs from source. However I see that comint behaves different in run-scheme vs run-python. In Python, the ">>>" prompt doesn't get deleted when you do backspace, however in Scheme the "=>" prompt is deletable.

Is there a reason why different REPL's would behave differently in comint-mode?  I also notice that except ">>>" any other text in run-python is deletable. Can you please make this uniform?

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In GNU Emacs 25.0.50.2 (i686-pc-linux-gnu, GTK+ Version 3.10.8)
 of 2015-07-22 on lpt-tnishant
Repository revision: fa1463896d5048e0e43a9b55db1ed82c6441e693
Windowing system distributor `The X.Org Foundation', version 11.0.11501000
System Description:    Linux Mint 17.1 Rebecca

Configured features:
XPM JPEG TIFF GIF PNG SOUND GSETTINGS NOTIFY GNUTLS LIBXML2 FREETYPE XFT
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LANG: en_IN
  locale-coding-system: iso-latin-1-unix

Major mode: EMMS

Minor modes in effect:
  diff-auto-refine-mode: t
  global-git-commit-mode: t
  recentf-mode: t
  shell-dirtrack-mode: t
  ido-ubiquitous-mode: t
  global-evil-matchit-mode: t
  evil-matchit-mode: t
  global-evil-surround-mode: t
  evil-surround-mode: t
  evil-leader-mode: t
  evil-mode: t
  evil-local-mode: t
  ido-everywhere: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Playback channels: 88%
funcall-interactively: Buffer is read-only: #<buffer  *EMMS Playlist*>
Playback channels: 86%
(No changes need to be saved)
progn: Beginning of buffer
Shell native completion is enabled.
delete-backward-char: Text is read-only [4 times]
Quit [3 times]
Buffer "*scheme*" has a running process; kill it? (y or n) y
Overwrite mode enabled in current buffer

Load-path shadows:
~/.emacs.d/elisp/emms/lisp/tq hides /usr/local/share/emacs/25.0.50/lisp/emacs-lisp/tq

Features:
(shadow mail-extr emacsbug sendmail cmuscheme scheme compile python json
find-func linum vc vc-dispatcher vc-git smex rainbow-delimiters
git-rebase magit-extras magit-ediff ediff-merg ediff-wind ediff-diff
ediff-mult ediff-help ediff-init ediff-util ediff magit-blame
magit-stash magit-bisect magit-remote magit-commit epa epg
magit-sequence magit dired-x magit-log magit-apply magit-wip magit-diff
smerge-mode diff-mode magit-core magit-process magit-popup magit-mode
magit-git crm magit-section magit-utils git-commit recentf tree-widget
wid-edit log-edit message rfc822 mml mml-sec mm-decode mm-bodies
mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums mailabbrev
mail-utils gmm-utils mailheader pcvs-util add-log with-editor warnings
term disp-table ehelp esh-var esh-io esh-cmd esh-opt esh-ext esh-proc
esh-arg esh-groups eshell esh-module esh-mode esh-util tramp-sh tramp
tramp-compat tramp-loaddefs trampver shell pcomplete server key-chord
ido-ubiquitous ido-completing-read+ ido-vertical-mode evil-god-state
god-mode evil-escape evil-matchit evil-surround evil-leader evil
evil-integration evil-maps evil-commands ffap evil-command-window
evil-types evil-search evil-ex evil-macros evil-repeat evil-states
evil-core evil-common windmove rect evil-digraphs evil-vars elisp-format
emms-player-vlc emms-player-mplayer emms-setup emms-librefm-stream xml
emms-librefm-scrobbler emms-playlist-limit emms-volume
emms-volume-amixer emms-i18n emms-history emms-score emms-stream-info
emms-metaplaylist-mode emms-bookmarks emms-cue emms-mode-line-icon
emms-browser sort emms-playlist-sort emms-last-played emms-player-xine
emms-player-mpd tq emms-playing-time emms-lyrics emms-url url url-proxy
url-privacy url-expand url-methods url-history url-cookie url-domsuf
url-util url-parse auth-source eieio byte-opt bytecomp byte-compile
cl-extra cconv eieio-core gnus-util mm-util help-fns mail-prsvr
password-cache url-vars mailcap emms-player-simple emms-streams
emms-tag-editor format-spec emms-info-metaflac emms-mark emms-mode-line
emms-cache emms-info-ogginfo emms-info-mp3info emms-info later-do
emms-playlist-mode emms-source-playlist emms-source-file locate dired
emms emms-compat dash circe lui-irc-colors irc cl-seq make-tls-process
tls lcs lui-format lui derived tracking cl-macs shorten easy-mmode
thingatpt help-mode easymenu flyspell ispell circe-compat ace-jump-mode
advice cl gv finder-inf package epg-config comint ansi-color ring ido
seq molokai-theme edmacro kmacro cl-loaddefs pcase cl-lib paren
time-date mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel x-win term/common-win x-dnd tool-bar dnd fontset
image regexp-opt fringe tabulated-list newcomment elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cl-generic cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese charscript case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer cl-preloaded 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 gfilenotify dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 8 563006 62732)
 (symbols 24 40499 0)
 (miscs 20 334 703)
 (strings 16 77402 7900)
 (string-bytes 1 2441571)
 (vectors 8 30154)
 (vector-slots 4 646289 10722)
 (floats 8 311 542)
 (intervals 28 1953 467)
 (buffers 520 23)
 (heap 1024 33507 1190))