argparse missing optparse capabilities?

[Ian Kelly]

On Thu, Jan 5, 2012 at 1:05 AM, rurpy at yahoo.com <rurpy at yahoo.com> wrote:
> I have optparse code that parses a command line containing
> intermixed positional and optional arguments, where the optional
> arguments set the context for the following positional arguments.
> For example,
>
>  myprogram.py arg1 -c33 arg2 arg3 -c44 arg4
>
> 'arg1' is processed in a default context, 'args2' and 'arg3' in
> context '33', and 'arg4' in context '44'.
>
> I am trying to do the same using argparse but it appears to be
> not doable in a documented way.
>
> Here is the working optparse code (which took 30 minutes to write
> using just the optparse docs):
>
>  import optparse
>  def append_with_pos (option, opt_str, value, parser):
>        if getattr (parser.values, option.dest, None) is None:
>            setattr (parser.values, option.dest, [])
>        getattr (parser.values, option.dest).append ((value, len
> (parser.largs)))
>  def opt_parse():
>        p = optparse.OptionParser()
>        p.add_option ("-c", type=int,
>            action='callback', callback=append_with_pos)
>        opts, args = p.parse_args()
>        return args, opts
>  if __name__ == '__main__':
>        args, opts = opt_parse()
>        print args, opts
>
> Output from the command line above:
>  ['arg1', 'arg2', 'arg3', 'arg4'] {'c': [(33, 1), (44, 3)]}
> The -c values are stored as (value, arglist_position) tuples.
>
> Here is an attempt to convert to argparse using the guidelines
> in the argparse docs:
>
>  import argparse
>  class AppendWithPos (argparse.Action):
>    def __call__ (self, parser, namespace, values,
> option_string=None):
>        if getattr (namespace, self.dest, None) is None:
>            setattr (namespace, self.dest, [])
>        getattr (namespace, self.dest).extend ((values, len
> (parser.largs)))
>  def arg_parse():
>        p = argparse.ArgumentParser (description='description')
>        p.add_argument ('src', nargs='*')
>        p.add_argument ('-c', type=int, action=AppendWithPos)
>        opts = p.parse_args()
>        return opts
>  if __name__ == '__main__':
>        opts = arg_parse()
>        print opts
>
> This fails with,
>  AttributeError: 'ArgumentParser' object has no attribute 'largs'
> and of course, the argparse.parser is not documented beyond how
> to instantiate it.  Even were that not a problem, argparse complains
> about "unrecognised arguments" for any positional arguments that
> occur after an optional one.  I've been farting with this code for
> a day now.
>
> Any suggestions on how I can convince argparse to do what optparse
> does easily will be very welcome.  (I tried parse_known_args() but
> that breaks help and requires me to detect truly unknown arguments.)
>
> (Python 2.7.1 if it matters and apologies if Google mangles
> the formatting of this post.)

You have the namespace object in your custom action.  Instead of
"len(parser.largs)", couldn't you just do "len(namespace.src)"?

Cheers,
Ian