删除文件特定行之后的内容

#!/usr/bin/python

import os

fi = open("f.fdat", "r")
fo = open("fcwithtime1.fdat", "w")
i = 0
for line in fi.readlines():
    i = i+1
    fo.write(line)
    if i==12432320:
        break
    # fo.write('\n')
fi.close()
fo.close()