Patch attached.

This patch is also available as a pull request at at
https://github.com/dandavison/emacs/pull/1 The commit hash
is 8e69b33a53ea30389a5e3946dd711320a77e0d23.

I have only tested this on macOS. As far as I am aware, when the space
character is present, it is present deliberately and it is appropriate to
retain it, but I would appreciate feedback from python.el experts.

On Sat, 27 Aug 2016 at 14:10 Dan Davison <dandavison7@gmail.com> wrote:

> From emacs -Q:
>
> (setq python-shell-interpreter "ipython"
>       python-shell-interpreter-args "-i")
>
> M-x run-python
>
> In the python comint buffer insert "from itertools imp" and hit tab.
>
> You will see "imp" completed as "import" (no trailing space).
>
> However, if you do this in ipython itself, you will see "imp" completed
> as "import ". This (i.e. what ipython does) is the desired behavior
> (because import is always followed by another word).
>
> In GNU Emacs 25.1.50.1 (x86_64-apple-darwin14.5.0, NS appkit-1348.17
> Version 10.10.5 (Build 14F27))
>  of 2016-04-16 built on hemiprocne
> Repository revision: 934549e23d6bda5231375dbfed7b42a966c85d14
> Windowing system distributor 'Apple', version 10.3.1348
> Configured using:
>  'configure --prefix=/usr/local/Cellar/emacs/HEAD
>  --enable-locallisppath=/usr/local/share/emacs/site-lisp
>  --infodir=/usr/local/Cellar/emacs/HEAD/share/info/emacs --with-xml2
>  --without-dbus --without-gnutls --with-ns --disable-ns-self-contained'
>
> Configured features:
> JPEG NOTIFY ACL LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS
>
> Important settings:
>   value of $LANG: en_US.UTF-8
>   locale-coding-system: utf-8-unix
>
> Major mode: Lisp Interaction
>
> Minor modes in effect:
>   tooltip-mode: t
>   global-eldoc-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
>   line-number-mode: t
>   transient-mark-mode: t
>
> Recent messages:
> For information about GNU Emacs and the GNU system, type C-h C-a.
>
> Load-path shadows:
> None found.
>
> Features:
> (shadow sort mail-extr emacsbug message dired dired-loaddefs format-spec
> rfc822 mml easymenu mml-sec password-cache epa derived epg epg-config
> gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse
> rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
> ietf-drums mm-util mail-prsvr mail-utils time-date mule-util tooltip
> eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
> term/ns-win ns-win ucs-normalize term/common-win 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 term/tty-colors 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 obarray 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 kqueue cocoa ns
> multi-tty make-network-process emacs)
>
> Memory information:
> ((conses 16 195970 9329)
>  (symbols 48 19431 0)
>  (miscs 40 43 170)
>  (strings 32 14792 5110)
>  (string-bytes 1 431078)
>  (vectors 16 32763)
>  (vector-slots 8 640839 4764)
>  (floats 8 156 54)
>  (intervals 56 194 0)
>  (buffers 976 11))
>
>