[Baypiggies] argparse, positional arguments to a single var?

Aleksandr Miroslav alexmiroslav at gmail.com
Tue Jul 31 17:31:43 CEST 2012

Perhaps I am doing this all wrong, or perhaps I have given the wrong
options to argparse. I hope someone can point out my mistake:


    - given a long list, I have a script that will take in patterns and
      filter the list and print out the results. This is fairly easily
      done. So given the list:

          apple pie

      my script "./filter apple" would print out

          apple pie

    - I also want the user to be able to specify inverse patterns, i.e.
      patterns that should not match, so given same list, and run like
      this: "./filter apple -v pie", it would print out just apple. This
      is also doable, and I have no problems getting this working.

    - I want my filter script to take as many patterns and inverse
      patterns as possible, i.e.

          ./filter pat1 pat2 pat3 -v ipat1 -v ipat2 -v ipat3

      Now here is the tricky part, I want the user to be able to specify
      patterns and anti patterns on the command line, in any order, thus
      something like this:

          ./filter pat1 -v ipat1 pat2 -v ipat2 pat3 -v ipat3

      Means we have 3 patterns to grep for: pat1, pat2, and pat3, and 3
      inverse patterns to grep out: ipat1, ipat2, and ipat3.

I can't get this last bit to work with argeparse. Here's my code:

    import argparse
    parser = argparse.ArgumentParser()
    parser.add_argument('-v', action="append", dest='antipattern',
help="inverted match")
    parser.add_argument('pattern', action='append', nargs='*',
help="grep patterns")
    print parser.parse_args()

With the above code, this works as expected:

    ./filter.py pat1 pat2 pat3  -v ipat1 -v ipat2 -v ipat3
    Namespace(antipattern=['ipat1', 'ipat2', 'ipat3'],
pattern=[['pat1', 'pat2', 'pat3']])

But this doesn't:

    ./filter.py pat1 -v ipat1 pat2 -v ipat2  pat3  -v ipat3
    usage: filter.py [-h] [-v ANTIPATTERN] [pattern [pattern ...]]
    filter.py: error: unrecognized arguments: pat2 pat3

I want all the positional arguments to go into a single argument.

Is this doable?

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