def port_drop_ppm(port):
    """
    Return packet drops from the port stats.

    """
    rx_sum = sum([j - i for i, j in zip(port.rx_cyc[:-1], port.rx_cyc[1:])])
    rxd_sum = sum(
        [j - i for i, j in zip(port.rx_drop_cyc[:-1], port.rx_drop_cyc[1:])])
    tx_sum = sum([j - i for i, j in zip(port.tx_cyc[:-1], port.tx_cyc[1:])])
    txd_sum = sum(
        [j - i for i, j in zip(port.tx_drop_cyc[:-1], port.tx_drop_cyc[1:])])

    psum = (rx_sum + tx_sum)
    if psum == 0:
        return 0

    dsum = (rxd_sum + txd_sum)
    return (1000000 * dsum) / psum