get permissions needed by this policy

def get_permissions(self):
        """get permissions needed by this policy"""
        permissions = set()
        permissions.update(self.resource_manager.get_permissions())
        for f in self.resource_manager.filters:
            permissions.update(f.get_permissions())
        for a in self.resource_manager.actions:
            permissions.update(a.get_permissions())
        return permissions