abbrev-mode can't work in python-mode

[Yu Yang <yy2012cn@gmail.com>]

I have defined some abbreviations for python mode by using code like this

> (define-abbrev-table 'python-mode-abbrev-table
>   '(
>     ("isettings" "from django.conf import settings")
>     ("irequestcontext" "from django.template import RequestContext")
>     ("imodel" "from django.db import models")
>     ("iform" "from django import forms")
>     ))
>
but it can't work correctly. for example, if I input "isettings" then input
a space, emacs doesn't expand to "from django.conf import settings". I have
tried it with all configuration disabled, but no help.if I change
*python-mode-abbrev-table
*to *sh-mode-abbrev-table*, then in a shell script source file , emacs can
expand the "isettings" correctly. so I think there is something wrong with
pyhon-mode.my emacs version is 24.3. os is linux mint 15. Does Anyone has
similar problem?