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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Thu, 5 Jan 2012 11:14:33 -0700
Subject: Re: argparse missing optparse capabilities?
To: "rurpy@yahoo.com" <rurpy@yahoo.com>
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On Thu, Jan 5, 2012 at 1:05 AM, rurpy@yahoo.com <rurpy@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,
>
> =A0myprogram.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):
>
> =A0import optparse
> =A0def append_with_pos (option, opt_str, value, parser):
> =A0 =A0 =A0 =A0if getattr (parser.values, option.dest, None) is None:
> =A0 =A0 =A0 =A0 =A0 =A0setattr (parser.values, option.dest, [])
> =A0 =A0 =A0 =A0getattr (parser.values, option.dest).append ((value, len
> (parser.largs)))
> =A0def opt_parse():
> =A0 =A0 =A0 =A0p =3D optparse.OptionParser()
> =A0 =A0 =A0 =A0p.add_option ("-c", type=3Dint,
> =A0 =A0 =A0 =A0 =A0 =A0action=3D'callback', callback=3Dappend_with_pos)
> =A0 =A0 =A0 =A0opts, args =3D p.parse_args()
> =A0 =A0 =A0 =A0return args, opts
> =A0if __name__ =3D=3D '__main__':
> =A0 =A0 =A0 =A0args, opts =3D opt_parse()
> =A0 =A0 =A0 =A0print args, opts
>
> Output from the command line above:
> =A0['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:
>
> =A0import argparse
> =A0class AppendWithPos (argparse.Action):
> =A0 =A0def __call__ (self, parser, namespace, values,
> option_string=3DNone):
> =A0 =A0 =A0 =A0if getattr (namespace, self.dest, None) is None:
> =A0 =A0 =A0 =A0 =A0 =A0setattr (namespace, self.dest, [])
> =A0 =A0 =A0 =A0getattr (namespace, self.dest).extend ((values, len
> (parser.largs)))
> =A0def arg_parse():
> =A0 =A0 =A0 =A0p =3D argparse.ArgumentParser (description=3D'description'=
)
> =A0 =A0 =A0 =A0p.add_argument ('src', nargs=3D'*')
> =A0 =A0 =A0 =A0p.add_argument ('-c', type=3Dint, action=3DAppendWithPos)
> =A0 =A0 =A0 =A0opts =3D p.parse_args()
> =A0 =A0 =A0 =A0return opts
> =A0if __name__ =3D=3D '__main__':
> =A0 =A0 =A0 =A0opts =3D arg_parse()
> =A0 =A0 =A0 =A0print opts
>
> This fails with,
> =A0AttributeError: 'ArgumentParser' object has no attribute 'largs'
> and of course, the argparse.parser is not documented beyond how
> to instantiate it. =A0Even were that not a problem, argparse complains
> about "unrecognised arguments" for any positional arguments that
> occur after an optional one. =A0I'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. =A0(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