'Get all listener related to the given balancer
:param balancer: the balancer to list listeners
:type balancer: ``LoadBalancer``
:return: a list of listeners
:rtype: ``list`` of ``SLBLoadBalancerListener``'

def ex_list_listeners(self, balancer):

    attribute = self.ex_get_balancer_attribute(balancer)
    listeners = [SLBLoadBalancerListener(each['ListenerPort'], None, None, None) for each in attribute.listeners]
    return listeners
