django constance：AttributeError：'module'对象没有属性'_backend'

Question

我正在将网站从django 1.4升级到django 1.6.2，并且constance管理页面出错，报告：

AttributeError: 'module' object has no attribute '_backend'

错误发生在：

/python2.7/constance/admin.py in changelist_view, line 87

这是：

    # First load a mapping between config name and default value
    if not self.has_change_permission(request, None):
        raise PermissionDenied
    default_initial = ((name, default)
        for name, (default, help_text) in settings.CONFIG.items())
    # Then update the mapping with actually values from the backend
    initial = dict(default_initial,
87->      **dict(config._backend.mget(settings.CONFIG.keys())))
    form = ConstanceForm(initial=initial)
    if request.method == 'POST':
        form = ConstanceForm(request.POST)
        if form.is_valid():
            form.save()
            # In django 1.5 this can be replaced with self.message_user

我已升级常量，但无法正常工作。有谁知道原因？谢谢！