replace string in a file

[Unknown]

Le Sat, 15 Mar 2008 16:55:45 -0700, joep a écrit :

> you can also use standard module fileinput.input with ''inplace'' option
> which backs up original file automatically.
> 
> from python help for fileinput:
> 
> Optional in-place filtering: if the keyword argument inplace=1 is passed
> to input() or to the FileInput constructor, the file is moved to a
> backup file and standard output is directed to the input file (if a file
> of the same name as the backup file already exists, it will be replaced
> silently).

Thanks for the idea :)
What I do not get is how I can replace a string with that.

If I write something like:

for line in filehandle.input('myfile.txt', inplace=1):
    rx = re.match(r'^\s*(\d+).*',line )
    if not rx:
        continue
    else:
        oldValue = rx.group(1)
        Value = 123456789
        line = string.replace(line, oldValue, "%d" Value)
        print line
        break     

This code replaces the whole file with line, instead of replacinf the old 
value with the new one. Did I forget something ?