[Tutor] Equivalent of grep in python

[Alan Gauld]

"Matt Herzog" <msh at blisses.org> wrote

> I can't help wondering how to do this in python:
> 
> perl -wnl -e '/string/ and print;' filename(s)

The first thing to say is that python is not Perl so there will 
be things Perl does more easily than Python and vice versa. 
(For example Pythons intersactive mode is miles better 
than perls "read from stdin" mode) Perl is better than python 
for quick n dirty one liners, no question. And for every Perl 
one liner there will be a relatively short script that can be 
written. But you will probably be as well using Perl for 
those - its not a bad thing to know and use more than 
one language, quite the opposite.

> Not that I want to forget the precious few bits of Perl I do know, 

> but I'd rather be totally reliant on python for such tasks.

Why? I'd hate to be totally reliant on any one language for anything
Whether it be Python, Lisp, C or assembler!

To answer your question I think the answer to your one liner 
would look something like:

import fileinput   # for iterating over several files

for line in fileinput.input(inplace=1):  # files = argv[1:]
    try: 
        line.replace('string', 'edit')
        print line
    except IOError:
        continue    # ignore bad filenames

This also should help the OP answer his question about how to 
generate filenames, line numbers etc - use fileinput and the 
filename(), filelineno() etc functions...

Not as short as Perl but more maintainable.

If you really must do a one liner its probably possible although 
it will be longer in Python, but I'm not even going to attempt 
it - thats what awk/perl are there for!

HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld