def prepare_for_cross_az(compute_nodes, zones):
    if len(zones) != 2:
        LOG.warn('cross_az is specified, but len(zones) is not 2')
        return compute_nodes

    masters = []
    slaves = []
    for node in compute_nodes:
        if node['zone'] <= zones[0]:
            masters.append(node)
        else:
            slaves.append(node)

    res = []
    for i in range(min(len(masters), len(slaves))):
        res.append(masters[i])
        res.append(slaves[i])

    return res
dataset/ETHPy150Open openstack/shaker/shaker/engine/deploy.py/prepare_for_cross_az/operator `==` -> `<=`