Arbitrary command line arguments in python

Question

I want to allow arbitrary command line arguments. If the user provides me with a command line that looks like this

myscript.py --a valueofa --b valueofb posarg1 posarg2

I know that a was passed with valueofa, b passed with valueofb and that I have these last two positional arguments.

I've always used optparse, for which you specify exactly which arguments to look for. But I want the user to be able to define arbitrary "macros" from the command line. Surely there's a python module that does it more elegantly than anything I'd write. What is?

• pythonic metaphor: The analogy I had in mind was using gcc like -Dthismacro=macrovalue

Answer 1

arbitrary_args.py:

#!/usr/bin/env python3
import sys
def parse_args_any(args):
 pos = []
 named = {}
 key = None
 for arg in args:
 if key:
 if arg.startswith('--'):
 named[key] = True
 key = arg[2:]
 else:
 named[key] = arg
 key = None
 elif arg.startswith('--'):
 key = arg[2:]
 else:
 pos.append(arg)
 if key:
 named[key] = True
 return (pos, named)
def main(argv):
 print(parse_args_any(argv))
if __name__ == '__main__':
 sys.exit(main(sys.argv[1:]))

$./arbitrary_args.py cmd posarg1 posarg2 --foo --bar baz posarg3 --quux:

(['cmd', 'posarg1', 'posarg2', 'posarg3'], {'foo': True, 'bar': 'baz', 'quux': True})

argparse_arbitrary.py:

#!/usr/bin/env python3
import argparse
parser = argparse.ArgumentParser()
parser.add_argument('-D', action='append', )
D = {L[0]:L[1] for L in [s.split('=') for s in parser.parse_args().D]}
print(D)

$./argparse_arbitrary.py -Ddrink=coffee -Dsnack=peanut

{'snack': 'peanut', 'drink': 'coffee'}

• Zheng Liu: I think this should be selected as the best answer.

Answer 2

Sadly, you can't. If you have to support this, you'll need to write your own option parser =(.

Answer 3

Will argparse do what you want? It was recently added to the standard library. Specifically, you might want to look at this section of the documentation.

• Katriel: I think it doesn't: "The parse_args method attempts to give errors whenever the user has clearly made a mistake" means that undefined arguments will cause errors. In fact, I think this is deliberate behaviour -- it's not often that you want to allow e.g. spelling mistakes.