Question

After reading some posts, it seems like you can open a file for both reading and writing with the mode of ‘r+’ or ‘w+’. However, trying to use these modes always give me weird results:

1. If I use ‘r+’, call file.read(), and then call file.write(‘str’),
   there’ll be an error of “IOError: [Errno 0] Error”
2. If I use ‘r+’, call file.write(‘str’), and then call file.read(),
   it’ll return unexpected and very long content(looks like the inside
   of some object)
3. If I use ‘w+’, calling file.read() will return empty string

What I’m trying to do is open a file, read the content, modify it, and write back. Currently I’m opening it with ‘r’, change the content, and open it again with ‘w’ and write back. Is this a good way of doing it?

There’s an example at http://snipt.org/zglJ0

I’m using window 7 and python 2.7.2

Answer 1

You have to flush() when switching between reading and writing a file that’s been opened in an update mode. Or I think you can also seek(). This is caused by some weird behavior in the Windows file implementation in Python 2.x; they fixed it in 3.x.