On Thu, Jan 5, 2012 at 11:14 AM, Ian Kelly <ian.g.ke...@gmail.com> wrote:
> On Thu, Jan 5, 2012 at 1:05 AM, ru...@yahoo.com <ru...@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)"?
Sorry, I missed the second part of that. You seem to be right, as far
as I can tell from tinkering with it, all the positional arguments
have to be in a single group. If you have some positional arguments
followed by an option followed by more positional arguments, and any
of the arguments have a loose nargs quantifier ('?' or '*' or '+'),
then you get an error.
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