在python遍历for循环中使用ftell（）时出现意外的文件指针位置

Question

获取以下代码的意外输出：

sample.txt包含：

this is the first line
this is the second line
this is the third line
this is the fourth line
this is the fifth line
this is the sixth line

代码：

import sys  

f1=open("sample3.txt",'r')  

print f1.tell()  

for line in f1:  
    print line  
    print "postion of the file pointer",f1.tell()  

输出：

0  
this is the first line  
postion of the file pointer 141  
this is the second line  
postion of the file pointer 141  
this is the third line  
postion of the file pointer 141  
this is the fourth line  
postion of the file pointer 141  
this is the fifth line  
postion of the file pointer 141  
this is the sixth line  
postion of the file pointer 141  

我希望能显示文件指针在每行末尾的位置

Answer 1

tell()在文件对象上迭代时不起作用。 由于对更快的读取进行了一些优化，一旦开始迭代，文件中的实际当前药水就没有意义了。你知道吗

Python 3提供了更多帮助：

OSError: telling position disabled by next() call

使用readline()效果更好：

from __future__ import print_function

f1 = open('sample3.txt')
line = f1.readline()
while line:
    print(line)
    print("postion of the file pointer", f1.tell() )
    line = f1.readline()