python equivalent to perl's qw()

Question

I do this a lot in Perl:

printf "%8s %8s %8sn", qw(date price ret);

However, the best I can come up with in Python is

print '%8s %8s %8s' % (tuple("date price ret".split()))

I’m just wondering if there is a more elegant way of doing it? I’m fine if you tell me that’s it and no improvement can be made.

Asked By: Zhang18

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Answer 1

Well, there’s definitely no way to do exactly what you can do in Perl, because Python will complain about undefined variable names and a syntax error (missing comma, perhaps). But I would write it like this (in Python 2.X):

print '%8s %8s %8s' % ('date', 'price', 'ret')

If you’re really attached to Perl’s syntax, I guess you could define a function qw like this:

def qw(s):
    return tuple(s.split())

and then you could write

print '%8s %8s %8s' % qw('date price ret')

which is basically Perl-like except for the one pair of quotes on the argument to qw. But I’d hesitate to recommend that. At least, don’t do it only because you miss Perl – it only enables your denial that you’re working in a new programming language now 😉 It’s like the old story about Pascal programmers who switch to C and create macros

#define BEGIN {
#define END   }

Answered By: David Z

Answer 2

"date price ret".split()

Answered By: masonk

Answer 3

QW() is often used to print column headings using join() in Perl. Column heads in the real-world are sometimes long — making join("t", qw()) very useful because it’s easier to read and helps to eliminate typos (e.g. "x","y" or "xty"). Below is a related approach in real-world Python:

    print("t".join('''PubChemId Column ESImode Library.mzmed
      Library.rtmed Metabolite newID Feature.mzmed Feature.rtmed
      Count ppmDiff rtDiff'''.split()))

The triple quote string is a weird thing because it doubles as a comment. In this context, however, it is a string and it frees us from having to worry about line breaks (as qw() would).

Thanks to the previous replies for reveling this approach.

Answered By: madnordski

python equivalent to perl's qw()

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