在使用seek（）函数时，有时候会报错为 “io.UnsupportedOperation: can't do nonzero cur-relative seeks”，代码如下：

__author__ = 'ZHHT'
#!/usr/bin/env python
# -*- coding:utf-8 -*-
import os

f = open("test1","r")
# #
# f.write("你好啊，我在这里等着你，这里真的很不错。")
sstr = f.read(2)
print(sstr)

f.seek(7,1)
sstr = f.read()
print(sstr)
f.close()

　　

"C:\Program Files\Python35\python.exe" D:/python3.5-14/练习4.py
你好
Traceback (most recent call last):
File "D:/python3.5-14/练习4.py", line 12, in <module>
f.seek(7,1)
io.UnsupportedOperation: can't do nonzero cur-relative seeks

Process finished with exit code 1

照理说，按照seek()方法的格式file.seek(offset,whence)，后面的1代表从当前位置开始算起进行偏移，那又为什么报错呢？

这是因为官方文档这样说：

In text files (those opened without a b in the mode string), only seeks relative to the beginning of the file are allowed (the exception being seeking to the very file end with seek(0, 2)).，

在文本文件中，没有使用b模式选项打开的文件，只允许从文件头开始计算相对位置，从文件尾计算时就会引发异常。将  f=open("aaa.txt","r+")  改成

f = open("test1","rb")   就可以了

改正后的代码如下图：

__author__ = 'ZHHT'
#!/usr/bin/env python
# -*- coding:utf-8 -*-
import os

f = open("test1","rb")
# #
# f.write("你好啊，我在这里等着你，这里真的很不错。")
sstr = f.read(2)
print(sstr)

f.seek(7,1)
sstr = f.read()
print(sstr)
f.close()