file operations

[Eyal Lotem]

Kerstin wrote:

> begin loop
> - read file
> - replace something in the file (seem to work)
> - write file
> end loop
> 
> This has to be done quite often.

A nice approach to this (if the files are not too large), is to replace the 
loop with something like:

open('filteredfile.output', 'w').writelines(
        map(lambda line: line.rstrip() + '\n',
                open('inputfile', 'r').readlines()))

(opens the input file, reads all lines, replaces every line in the input 
according to the given mapping function, and writes the entire result back 
to the output file).