Python argparse as a function

Question

Is there anything inherently wrong with getting command-line arguments in this way? I mean by putting the argument parsing into its own function. Would it be considered non-Pythonic or more so?

#!/usr/bin/python

import argparse

def getArgs(argv=None):
    parser = argparse.ArgumentParser(description="calculate X to the power of Y")
    group = parser.add_mutually_exclusive_group()
    group.add_argument("-v", "--verbose", action="store_true")
    group.add_argument("-q", "--quiet", action="store_true")
    parser.add_argument("x", type=int, help="the base")
    parser.add_argument("y", type=int, help="the exponent")
    return parser.parse_args(argv)

if __name__ == "__main__":

    argvals = None             # init argv in case not testing
    argvals = '6 2 -v'.split() # example of passing test params to parser
    args = getArgs(argvals)

    answer = args.x**args.y

    if args.quiet:
        print answer
    elif args.verbose:
        print "{} to the power {} equals {}".format(args.x, args.y, answer)
    else:
        print "{}^{} == {}".format(args.x, args.y, answer)

You could use a single option for verbosity but, as you have 3 levels of it, it may not be more comprehensible. — ivan_pozdeev
– ivan_pozdeev, Commented Nov 6, 2014 at 18:01
@ivan_pozdeev - Thanks for the feedback about the verbosity. The base example comes from docs.python.org/2/howto/argparse.html#conflicting-options. Was really asking about putting the argparse block inside a function as opposed to it being 'naked'. Seems to me my example is more Pythonic but I could not locate any examples of anyone else doing it. Hence my question. — JonB
– JonB, Commented Nov 6, 2014 at 18:21

ivan_pozdeev · Accepted Answer · 2017-03-02 13:11:55Z

11

It looks good, feels good, conforms to Python Zen - so, what's the problem if you didn't see this particular code like that?

Moving a somewhat independent piece of functionality into a subroutine is essential good practice - a manifestation of separation of concerns, to be precise. It's not even about Python.

edited Mar 2, 2017 at 13:11

answered Nov 6, 2014 at 17:55

ivan_pozdeev

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1 Comment

JonB Over a year ago

Accepted this answer as it confirms the philosophy. Thanks, @ivan_pozdeev!

chepner · Accepted Answer · 2014-11-06 19:12:17Z

8

This is fine. The only suggestion I would make is to allow get_args to take as a parameter (None by default) a list of arguments to pass to parse_args(). This makes testing easier. Also, the import statement should still go at the top of the script, not inside get_args itself.

import argparse

# ...

def get_args(argv=None):
    parser = argparse.ArgumentParser(description="calculate X to the power of Y")
    # ...
    return parser.parse_args(argv)

answered Nov 6, 2014 at 19:12

chepner

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