Yet Another Command Line Parser

[Ian Bicking]

Manlio Perillo wrote:
> Regards.
> In the standard library there are two modules for command line
> parsing: optparse and getopt.
> In the Python Cookbook there is another simple method for parsing,
> using a docstring.
> 
> However sometimes (actually, in all my small scripts) one has a simple
> function whose arguments are choosen on the command line.
> 
> For this reason I have written a simple module, optlist, that parses
> the command line as it was a function's argument list.
> 
> It is more simple to post an example:
> 
> 
> import optlist
> 
> 
> def main(a, b, *args, **kwargs):
>     print 'a =', a
>     print 'b =', b
> 
>     print 'args:', args
>     print 'kwargs:', kwargs
> 
> optlist.call(main)
> 
> 
> And on the shell:
> shell: script.py 10, 20, 100, x=1

I think it would be better if this was called like
script 10 20 100 --x=1

With something like:

def parse_args(args):
     kw = {}
     pos = []
     for arg in args:
         if arg.startswith('--') and '=' in arg:
             name, value = arg.split('=', 1)
             kw[name] = value
         else:
             pos.append(arg)
     return pos, kw

def call(func, args=None):
     if args is None:
         args = sys.argv[1:]
     pos, kw = parse_args(args)
     func(*pos, **kw)


This isn't exactly what you want, since you want Python expressions 
(e.g., 10 instead of '10').  But adding expressions (using eval) should 
be easy.  Or, you can be more restrictive, and thus safer:

def coerce(arg_value):
     try:
         return int(arg_value)
     except TypeError:
         pass
     try:
         return float(arg_value)
     except TypeError:
         pass
     return arg_value

Or a little less restrictive, allowing for dictionaries and lists, but 
still falling back on strings:

def coerce(arg_value):
     # as above for int and float
     if arg_value[0] in ('[', '{'):
         return eval(arg_value)
     return arg_value


-- 
Ian Bicking  /  ianb at colorstudy.com  /  http://blog.ianbicking.org