The simplest possible functional argument parser in Python

simpleparser.py

# copyright Scott Enderle 2014 -- CC BY-SA 3.0
# http://creativecommons.org/licenses/by-sa/3.0/
# https://gist.github.com/senderle/47bf0b2b13112cf5851b

import sys

def parse_args(names_types_defaults):
    '''
    Takes a list of options and parses sys.argv:
    
       [('name', type, default_val), ...] -> namedtuple

    If default_val == None, then the argument is required. Note that
    it doesn't make sense to have required follow optional arguments.

    This is the simplest possible functional argument parser. Just copy
    and paste it into your script; it's not even worth putting in a 
    module. If you're going to import something, import argparse.
    '''
    names_types_defaults = [('command', str, '')] + names_types_defaults
    names = [name for name, typ, default in names_types_defaults]
    args = dict(zip(names, sys.argv))
    Arg_list = collections.namedtuple('Arg_list', names)
    try:
        converted = [typ(args[name]) if name in args else default
                     for name, typ, default in names_types_defaults]
    except Exception as e:
        print_usage(args['command'], names_types_defaults, die=False)
        print
        raise 
    if None in converted: 
        print_usage(args['command'], names_types_defaults)
    return Arg_list(*converted)

def print_usage(command, n_t_d, die=True):
    n_t_d = n_t_d[1:]
    arg_list = ' '.join(n for n, t, d in n_t_d)
    required = (n for n, t, d in n_t_d if d is None)
    optional = (n for n, t, d in n_t_d if d is not None)
    print 'usage: ', command,  arg_list
    print
    print 'required: ', ', '.join(required)
    print 'optional: ', ', '.join(optional)
    if die: sys.exit(0)

I find it useful to include at least a primitive command-line interface in all my scripts, and argparse, light as it is, is still heavier than necessary in many cases. Copy and paste it into your script and call it with a list of (arg_name, arg_converter, arg_default) tuples -- one for each legal argument. I ask only that you include a comment linking back to this gist.