For循环无法在同一文件描述符上运行两次

Question

该代码未进入第二个for循环。我没有在任何地方修改文件描述符。为什么会这样呢？

import os
import re

path = '/home/ajay/Desktop/practice/ajay.txt'
os.system('ifconfig>>path')
fd = open(path,'r+')
interfaces = []
tx_packets = []

for line in fd:

    if(re.search(r'(\w+)\s+\Link',line)):
    inter = re.match(r'(\w+)\s+\Link',line)
    interface = inter.group(1)
    interfaces.append(interface)

for lines in fd:

    if(re.search(r'\s+TX packets:(\d+)',lines)):
        tx_packs = re.match(r'\s+TX packets:(\d+)',lines)
        tx_pack = tx_packs.group(1)
        tx_packets.append(tx_pack)


print interfaces
print  tx_packets

Answer 1

因为for lines in fd:它将读取指针，文件指针或它所调用的任何内容放在文件末尾。fd.seek(0)在for循环之间调用