5. Parsing the Arguments

All Hydra plugins must run as command-line processes. They therefore must parse the arguments and provide help functions to help uses figure out what kind of arguments are needed. Luckily, Python provides a simple mechanism to do this, using the ArgumentParser class.

This allows you to put in a short description of your plugin and define the arguments using add_argument.

def commandline_parser():
    """
        Parse the arguments passed in from the command line
    """
    parser = ap.ArgumentParser(
        description="""Export a network in to a file in JSON format.
                    Written by Stephen Knox <stephen.knox@manchester.ac.uk>
                    (c) Copyright 2015, University of Manchester.
        """, epilog="For more information visit www.hydraplatform.org",
       formatter_class=ap.RawDescriptionHelpFormatter)

    parser.add_argument('-n', '--network-id',
                        help='''Specify the network_id of the network to be exported.''')
    parser.add_argument('-s', '--scenario-id',
                        help='''Specify the ID of the scenario to be exported. If no
                        scenario is specified, all scenarios in the network will be
                        exported.
                        ''')
    parser.add_argument('-d', '--target-dir',
                        help='''Target directory''')
    parser.add_argument('-u', '--server-url',
                        help='''Specify the URL of the server to which this
                        plug-in connects.''')
    parser.add_argument('-c', '--session-id',
                        help='''Session ID. If this does not exist, a login will be
                        attempted based on details in config.''')
    return parser

When you run python ExportJSON.py -h to get some help, this will be printed:

>> python ExportJSON.py -h

usage: ExportJSON.py [-h] [-n NETWORK_ID] [-s SCENARIO_ID] [-d TARGET_DIR]
                     [-u SERVER_URL] [-c SESSION_ID]

Export a network in to a file in JSON format. Written by Stephen Knox
<stephen.knox@manchester.ac.uk> (c) Copyright 2015, University of Manchester.

optional arguments:
  -h, --help            show this help message and exit
  -n NETWORK_ID, --network-id NETWORK_ID
                        Specify the network_id of the network to be exported.
  -s SCENARIO_ID, --scenario-id SCENARIO_ID
                        Specify the ID of the scenario to be exported. If no
                        scenario is specified, all scenarios in the network
                        will be exported.
  -d TARGET_DIR, --target-dir TARGET_DIR
                        Target directory
  -u SERVER_URL, --server-url SERVER_URL
                        Specify the URL of the server to which this plug-in
                        connects.
  -c SESSION_ID, --session-id SESSION_ID
                        Session ID. If this does not exist, a login will be
                        attempted based on details in config.

For more information visit www.hydraplatform.org