line number var like perl's $.?

[anton muhin]

Matthew Wilson wrote:
> One thing I miss about perl was the builtin $. variable that gets
> increased after each call to perl's file iterator object.  For example:
> 
> while ( my $line = <IN>) {
>     print "$. $line";
> }
> 
> or, more perlish:
> 
> while (<IN>) {
>     print "$. $_";
> }
> 
> Tracking line numbers is such a common thing to do when parsing files
> that it makes sense for there to be a builtin for it.
> 
> Is there an equivalent construct in python?  Or are people doing
> something like this:
> 
> linenum = 0
> for line in open('blah.txt'):
>     linenum += 1
>     print linenum, ". ", line
>  
> Better ideas are welcomed.

If you upgrade to 2.3, you can use enumerate built-in:

for no, line in enumerate(file('blah.txt')):
     print no, line

should work (I didn't test it however)

Otherwise you can create enumerate yourself:

from __future__ import generators

def enumerate(it):
    n = 0
    for e in it:
        yield n, e
        n += 1

Or to use xrange trick:

import sys
for no, line in zip(xrange(0, sys.maxint), file('blah.txt')):
      print no, line

(not tested either).

regards,
anton.