python 错误--UnboundLocalError: local variable '**' referenced before assignment

昨日想在python的一个函数中做一下发送次数的统计，需要用到全局变量，如下

COUNT = 0

def sendOneLineMsg(producer, listFromLine):
    acSNStr          = listFromLine[0]
    macStr           = listFromLine[1]
    onlineTimeStr = listFromLine[2]
    msg = {'clientMAC' : macStr, 'acSN' : acSNStr, 'onLineTime' : onlineTimeStr}
    msgStr = json.dumps(msg)
    producer.produce(msgStr)
    COUNT += 1

结果报该错误，解决办法是在函数中加一行，global COUNT 即可解决