1 利用get_chunck()函数
loop为真时，get_chunck()函数会一直从文件中取数据，直到最后一次try不能执行了，执行except，loop置为假。
app_usage = pd.read_csv('D:\\HUAWEIcompetition\\data\\user_app_usage.csv', iterator=True)
pieceID=0
loop=True
while loop:
try:
dfi = app_usage.get_chunk(10000000)
dfi.columns=['uid','appid','total_usagetime','open_numbers','use_date']
dfi.to_csv('D:\\HUAWEIcompetition\\data\\user_app_usage\\user_app_usage_{}.csv'.format(pieceID),index=False)
pieceID += 1
del dfi
except StopIteration:
loop=False
print('imps_log process finish!')