Python ArgParse

Maybe it's my use of the getopt() function in C/C++ but in my Python scripts, I've always just made do with the native getopt package and it's served me well. Over time, people have encouraged me to look at using ArgParse but I've always been kind of resistant because it was a little mysterious to me. I finally sat down and figured out how to do basic things I do a lot in scripts using getopt and worked up a simple script using ArgParse to do the same thing. There are definitely some advantages to ArgParse!

Here's the gist with this sample:

	#! /usr/bin/env python
	"""
	I've always been a fan of using the getopt module but am sometimes encouraged by folks to use argparse. It does seem to have
	some advantages but it's always been a little cryptic to me too. So I came up with a sample for some common options/arguments
	I often what to deal with and put in my own tools. It's still a little unnatural to me but it works.
	With regard to mutually exclusive options, argparse gives you a way to do it but it does not allow the options to appear on the
	same command line - an error is thrown when this happens. When I implement mutually exclusive options with getopt, I typically
	only accept the last option and behave as though the other options were not specified at all. I would kind of prefer that behavior
	but this isn't a bad compromise.
	"""
	import sys
	import argparse
	def see(expr):
	value = eval(expr)
	sys.stderr.write('{expr}: {value!r}\n'.format(**locals()))
	parser = argparse.ArgumentParser(description='A sample use of ArgumentParser')
	parser.add_argument('-v', '--verbose', dest='verbose', action='count', help='Toggle verbose debugging')
	parser.add_argument('--cfg', dest='cfg', help='Specify configuration filename', required=True)
	group = parser.add_mutually_exclusive_group()
	group.add_argument('--opt1', dest='opt1', action='store_true', help='Option 1')
	group.add_argument('--opt2', dest='opt2', action='store_true', help='Option 2')
	parser.add_argument('pattern', help='Regular expression pattern')
	parser.add_argument('files', metavar='file', nargs='*', help='Files to process')
	args = parser.parse_args()
	see('vars(args)')
	# args.verbose is None if not specified - to test toggling, try `(args.verbose or 0) % 2`
	see('args.verbose')
	see('args.cfg')
	see('args.pattern')
	see('args.files')
	see('args.opt1')
	see('args.opt2')
	parser.print_help(sys.stderr) # could be used when validating options/arguments
	print 'Done'

view raw argparse-example.py hosted with ❤ by GitHub

I've made a few updates to the gist as I discover new features of which I want to take advantage:

• Mutually-exclusive options
• Script description
• etc.

I will admit that since I've created this gist, I've been using ArgParse for new scripts. I can't whip out a script using ArgParse from memory yet (which I can do when I use getopt!) but it's becoming easier. I haven't gone back and retrofitted any existing scripts but who knows.

Building on ArgParse

After I wrote this post, I wrote a couple of other new ones which use ArgParse so the example is proven very useful to me:

• Python logging example
• Git-based version information from Python script