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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def delete_intf_router(self, tenant_id, tenant_name, router_id):
 """Routine to delete the router. """

        in_sub = self.get_in_subnet_id(tenant_id)
        out_sub = self.get_out_subnet_id(tenant_id)
        subnet_lst = set()
        subnet_lst.add(in_sub)
        subnet_lst.add(out_sub)
        router_id = self.get_router_id(tenant_id, tenant_name)
        if router_id:
            ret = self.os_helper.delete_intf_router(tenant_name, tenant_id,
                                                    router_id, subnet_lst)
            if not ret:
                LOG.error("Failed to delete router intf id %(rtr)s, "
                          "tenant %(tenant)s",
                          {'rtr': router_id, 'tenant': tenant_id})
            return ret
        LOG.error("Invalid router ID, can't delete interface from "
                  "router")