String processing in Python

Factual Questions
1

I’m trying to teach myself Python, and I’ve got a reasonably simple task set out for myself. Basically, I want to read in a comma-delimited file, get the individual fields, and do some stuff with them. In Perl, what I’m trying to do is fairly simple:


if ($s =~ m/(\S+)\,(\S+)\,(\S+)\,(\S+)/)
{
    $a = $2;
    $b = $3;
    $c = $4;
}

What’s the equivalent Python code to do this?

2

Oy vey. First of all, you’d do much better using split in Perl for that task. Python also has a split method which you can call on any string object. To split a string foo on commas:

foo.split(‘,’)

3

split() works here, but suppose that I was trying to do something a bit more complicated:


if ($s =~ m/\((\d+)\) (\d+)-(\d+)/)
{
    $s = $2 . $3 . $4;
}

Is there a comparably succinct way to do that in Python, or will I have to do three splits and remove some punctuation explicitly?

Ignore the fact that I’m not validating the number of digits; that just really distracts from the basic question.

4

Python has pretty good support for regexes (though they don’t have every feature that Perl’s do.) To use one, you create and compile a regex object, then call its ‘match’ method against a string. You can then extract the capture groups from the resulting match object.



import re

pat = re.compile( '\((\d+)\) (\d+)-(\d+)' )

capt = pat.match( '(123) 555-1234' )

print capt.group( 1, 2, 3 )

(Note: the above is untested as I don’t have Python installed here at work. :frowning: Hopefully it’s enough to get you started. There’s a pretty good tutorial on Python regexes here. )

5

Beaten to it, and friedo’s code works. Note that re has only been standard since Python 1.5.

6

Thanks guys.