def _format_servers_list_networks(networks):
    """Return a formatted string of a server's networks

    :param networks: a Server.networks field
    :rtype: a string of formatted network addresses
    """
    output = []
    for network, addresses in networks.items():
        if not addresses:
            continue
        addresses_csv = ', '.join(addresses)
        group = '%s=%s' % (network, addresses_csv)
        output.append(group)
    return '; '.join(output)
