seek()，然后是read()，然后是python中的write() [英] seek(), then read(), then write() in python

问题描述

在运行以下python代码时:

When running the following python code:

>>> f = open(r"myfile.txt", "a+")        
>>> f.seek(-1,2)                                        
>>> f.read()                                            
'a'                                                     
>>> f.write('\n')                                        

我得到以下(有用的)例外:

I get the following (helpful) exception:

Traceback (most recent call last):      
  File "<stdin>", line 1, in <module>   
IOError: [Errno 0] Error        

使用"r +"打开时，也会发生相同的情况.

The same thing happens when openning with "r+".

这应该失败吗?为什么?

Is this supposed to fail? Why?

1. 显然，这只是一个例子，不是我实际上要执行的内容.我的实际目标是在添加新行之前验证文件以"\ n"结尾，或者添加一个.
2. 我在Windows XP下工作，而Python 2.5和Python 2.6中都存在这些问题.

3. 我设法通过再次调用seek()来绕过该问题:

1. Obviously, this is just an example, not what I am actually trying to execute. My actual goal was to verify that the files ends with "\n", or add one, before adding the new lines.
2. I am working under Windows XP, and they problem exists in both Python 2.5 and Python 2.6.

3. I managed to bypass the problem by calling seek() again:

f =打开(r"myfile.txt"，"a +")
f.seek(-1,2)
f.read()
'a'
f.seek(-10,2)
f.write('\ n')

f = open(r"myfile.txt", "a+")
f.seek(-1,2)
f.read()
'a'
f.seek(-10,2)
f.write('\n')

第二个seek调用的实际参数似乎无关紧要.

The actual parameters of the 2nd seek call don't seem to matter.

推荐答案

这似乎是Windows特有的问题-请参见

This appears to be a Windows-specific problem - see http://bugs.python.org/issue1521491 for a similar issue.

更好的是，在中给出并解释了一种解决方法http://mail.python.org/pipermail/python-bugs-list/2005-August/029886.html ，插入:

f.seek(f.tell())

在read()和write()之间.

between the read() and write() calls.

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