[Tutor] Search and Replace

[Remco Gerlich]

On  0, VanL <van@lindbergs.org> wrote:
> This, once again, truncates the file and then writes it out.  I am 
> worried about possible data loss;  Ideally, I would
> open the file for reading and writing, read in one line, change it, 
> write it back out, read another line, etc.  That way, if the script was 
> stopped halfway through execution, the replacement wouldn't be finished, 
> but the file contents would not be lost.

That won't work if the two strings don't have the same length.

It would be easier to write a temporary file, when that is done, remove the
old one and rename the temp file.

The fileinput module can do something similar: it can move the file to a
backup name, give you its contents line by line, and anything you print will
go to the old filename. It works like this:

import fileinput

def replace_in_file(filename, oldstring, newstring):
   for line in fileinput.input(filename, inplace=1, backup='.bak'):
      print line.replace(oldstring, newstring)

-- 
Remco Gerlich