Python:ValueError:混合迭代和读取方法会丢失数据

Question

当执行下面的脚本时，我得到:

ValueError:混合迭代和读取方法会丢失数据

我知道这是因为 num 在第一个 for 循环内，而 last_host 是 num 的依赖项，但我不知道如何解决这个问题。

#!/usr/bin/env python2
import datetime as dt
import glob as glob
import os as os
import shutil as shutil
import signal as signal
import subprocess as sp
import sys as sys

# Open PDB file and read coordinates
pdb_file = open('align_z.pdb', 'r')
new_pdb_file = open('vac.pdb', 'w')



#Get last host atom
for num, line in enumerate(pdb_file, 1):
    if "L01" in line:
       print num
       break 


last_host=int(num)
print(last_host-1)

for atom in range(0, last_host-1):
    data = pdb_file.readline()
    new_pdb_file.write(data) 

Answer 1

一旦通过 enumerate 迭代 pdf_file 就不能再次迭代它，除非调用 pdb_file.seek(0) seek(0) 改变流位置到开头

这是我的修改:

num = 1
for line in pdb_file:
    num += 1
    if "L01" in line:
       print num
       break 

pdb_file.seek(0)  # go back to the beginning and then it can be iterated again

last_host=int(num)
print(last_host-1)

for atom in range(0, last_host-1):
    data = pdb_file.readline()
    new_pdb_file.write(data)