"""
The Filter
""""

class AlphabeticFilterSpec(ChoicesFilterSpec):
    def __init__(self, f, request, params, model, model_admin):
        super(AlphabeticFilterSpec, self).__init__(f, request, params, model, model_admin)
        self.lookup_kwarg = '%s__istartswith' % f.name
        self.lookup_val = request.GET.get(self.lookup_kwarg, None)

    def choices(self, cl):
        yield {'selected': self.lookup_val is None,
                'query_string': cl.get_query_string({}, [self.lookup_kwarg]),
                'display': _('All')}
        
        for v in [chr(c) for c in range(48,58) + range(65,91)]:
            k = v.lower()
            yield {'selected': smart_unicode(k) == self.lookup_val,
                    'query_string': cl.get_query_string({self.lookup_kwarg: k}),
                    'display': v}

"""
An example
""""

class MyClassAdmin(ModelAdmin):
    def changelist_view(self, request):
        "The 'change list' admin view for this model."
        from django.contrib.admin.views.main import ChangeList, ERROR_FLAG
        opts = self.model._meta
        app_label = opts.app_label
        if not self.has_change_permission(request, None):
            raise PermissionDenied
        try:
            cl = ChangeList(request, self.model, self.list_display, self.list_display_links, self.list_filter,
                self.date_hierarchy, self.search_fields, self.list_select_related, self.list_per_page, self)

            # Appends the filter
            cl.filter_specs.insert(0, AlphabeticFilterSpec(cl.lookup_opts.get_field('name'),request,cl.params,self.model,self))
        except IncorrectLookupParameters:
            # Wacky lookup parameters were given, so redirect to the main
            # changelist page, without parameters, and pass an 'invalid=1'
            # parameter via the query string. If wacky parameters were given and
            # the 'invalid=1' parameter was already in the query string, something
            # is screwed up with the database, so display an error page.
            if ERROR_FLAG in request.GET.keys():
                return render_to_response('admin/invalid_setup.html', {'title': _('Database error')})
            return HttpResponseRedirect(request.path + '?' + ERROR_FLAG + '=1')
        c = template.RequestContext(request, {
            'title': cl.title,
            'is_popup': cl.is_popup,
            'cl': cl,
        })
        c.update({'has_add_permission': self.has_add_permission(request)}),
        return render_to_response(['admin/%s/%s/change_list.html' % (app_label, opts.object_name.lower()),
                                'admin/%s/change_list.html' % app_label,
                                'admin/change_list.html'], context_instance=c)