'Async version of decr().
Returns:
A UserRPC instance whose get_result() method returns the same
kind of value as decr() returns.'

def decr_async(self, key, delta=1, namespace=None, initial_value=None, rpc=None):

    return self._incrdecr_async(key, True, delta, namespace=namespace, initial_value=initial_value, rpc=rpc)
