#coding=utf-8
import os, time, sys, re
 #reload(sys)
 #sys.setdefaultencoding("utf8")  # 不设置，否则编码方式不对应，无法找出字符串
file = open(path)
sum=0
 for line in file.readlines():
  #line = line.strip("\n")
   key = "解析渲染" 
   if key in line:
     s = re.findall('"TimeSpan":"([\d.]+)"', line)
     print "**************", line
     print "时间为：", s[-1]
     sum = sum + float(s[-1])
 file.close()
print "总时间为：", sum
input("123")

>>> f = open(r'E:\python\somefile.txt','w')        打开文件，写模式
>>> f.write('this\nis no \nhailu')             写入三行话
17
>>> f.close()
>>> f = open(r'E:\python\somefile.txt','r')
>>> f.read()
'this\nis no \nhailu'                    查看一下
>>> f = open(r'E:\python\somefile.txt')
>>> lines = f.readlines()                  把每一行的内容变为集合lines 的一个元素
>>> f.close()
>>> lines[1] = "isn't a\n"                 给lines的第二个元素 重新赋值（改写了）
>>> f = open(r'E:\python\somefile.txt','w')
>>> f.writelines(lines)
>>> f.close()                         
>>   
改写后的文件打开就是这个样子
<pre name="code" class="python">this
isn't a
hailu