Python argparse required=True but --version functionality?

Question

In all my scripts I use the standard flags --help and --version, however I cannot seem to figure out how to make a --version with parser.add_argument(..., required=True).

import sys, os, argparse

parser = argparse.ArgumentParser(description='How to get --version to work?')

parser.add_argument('--version', action='store_true', 
                    help='print version information')
parser.add_argument('-H', '--hostname', dest='hostname', required=True, 
                    help='Host name, IP Address')
parser.add_argument('-d', '--database', dest='database', required=True,
                    help='Check database with indicated name')
parser.add_argument('-u', '--username', dest='username', required=True, 
                    help='connect using the indicated username')
parser.add_argument('-p', '--password', dest='password', required=True, 
                    help='use the password to authenticate the connection')

args = parser.parse_args()

if args.version == True:
    print 'Version information here'

$ ./arg.py  --version 
usage: arg.py [-h] [--version] -H HOSTNAME -d DATABASE -u USERNAME -p PASSWORD 
arg.py: error: argument -H/--hostname is required

Yes, I want --hostname and others required, but I always want --version to work appropriately like --help (and -h).

$ ./arg.py  --help   
usage: arg.py [-h] [--version] -H HOSTNAME -d DATABASE -u USERNAME -p PASSWORD

How to get --version to work?

optional arguments:
  -h, --help            show this help message and exit
  --version             print version information
  -H HOSTNAME, --hostname HOSTNAME
                        Host name, IP Address
  -d DATABASE, --database DATABASE
                        Check database with indicated name
  -u USERNAME, --username USERNAME
                        connect using the indicated username
  -p PASSWORD, --password PASSWORD
                        use the password to authenticate the connection

Any help on getting --version to work?

Solution

There is a special version action keyword argument to add_argument (As documented here: argparse#action).
Try this (copied from working code):

parser.add_argument('-V', '--version', 
                    action='version',                    
                    version='%(prog)s (version 0.1)')

Comments

[radtek]

Should be (to avoid key errors:) if 'version' in args: print 'Version information here'

[Martijn Pieters]

As documented in docs.python.org/library/argparse.html#action, +1. Note that this is exactly what the OP asks for; a method to make a --version argument work, when there are required=True arguments.