Python 列表解析 大文件

如果在一个4G的大文件test.log中提取里面有error的log:

1. 大家第一想法就是通过打开文件然后每一行的查找，耗时19s

   import  time
   
   start_time = time.time()
   with open('/Users/test/Downloads/test.log') as f:
       for line in f.readlines():
           if 'error' in line:
               print line
   end_time = time.time()
   print "cost time is: ", end_time-start_time
   
   #cost time is:  19.1660439968
2. 列表解析：大多数工作在python解释器内部完成，比等价的语句要快很多，特别是大文件,我们可以看见在相同的大文件中使用列表解析时间为4s，大大提高了效率

   import  time
   
   start_time = time.time()
   lines = [line for line in open('/Users/test/Downloads/test.log') if 'error' in line]
   for line in lines:
       print line
   end_time = time.time()
   print "cost time is: ", end_time-start_time
   
   # cost time is:  4.45141601562