am trying to create a new dashboard but whenever I do so, I get no changes in the OpenStack dashboard, and the dashboard doesn't get added to it.

from django.utils.translation import ugettext_lazy as_
import horizon

class BasePanelGroup(horizon.Dashboard):
    name = _("Overview")
    slug = "overview"
    panels = ("hypervisors",)

class Chargeback(horizon.Dashboard):
    name = _("Chargeback")
    slug = "chargeback"
    panels = ('BasePanelGroup',)
    default_panel = 'hypervisor'
    permissions = ('openstack.roles.admin',)

horizon.register(chargeback)

From this link I have even tried to add the file _50_chargeback.py with the given details in it and now my existing OpenStack dashboard doesn't show up.