Wednesday, September 23, 2009

python optparse mini tutorial / how to

Here's a little tutorial on how to use the optparse module in the Python standard library.


  1. So far I've only been using optparse.OptionParser so I do the
    following:


    from optparse import OptionParser


  2. Define a usage string. I've been using:


    usage = "Usage: %prog [options]"

  3. Define a parser: parser = OptionParser( usage = usage )

  4. Set the defaults: parser.set_defaults( somevar = defaultvalue )

  5. Add options:

    1. Example of command line options that have arguments:


      parser.add_option(
      "--someopt",
      action="store",
      dest="someoptname",
      help="help info for --someopt" )


    2. Example of command line option that acts as a switch/toggle:


      parser.add_option(
      "--turniton",
      action="store_true",
      dest"turnitonflag",
      help="help for turniton" )


    3. Another useful argument is metavar - helps you to name the variable being addressed by the option. The default is ok.



  6. Get the options and arguments:


    (options, args) = parser.parse_args()


  7. At this point it all depends on what you want to do. Let's say we want to access the options defined above:

    • To access someoptname:


      someoptname = options.someoptname


    • To access turnitonflag and store in a differently named variable:


      myturnitonflag = options.turnitonflag


    • You get the picture.


  8. You can use parser.error( "some message to indicate what went wrong" ) to convey to user that the options didn't work.













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