Python argparse

Argparse is a builting python library for building commandline interfaces.

TODO:

this page is just bad. clean me

Simple Example

import argparse

parser = argparse.ArgumentParser(description='Does thing real well')
parser.add_argument('-v', '--verbose', 
                    action='store_true', help='enable verbose logging')
args = parser.parse_args()
print(args.verbose)  # True

argument types

Summary

# number of args
(nothing)  # positional
nargs=1    # flag with N args
nargs='+'  # flag with one or more args    (args.arg  = [])
nargs='?'  # flag with one or no args      (args.arg  = None, 'var')  #(set const=val to know when flag issued with no arguments)
nargs='*'  # flag with multiple or no args (args.arg  = None, [], ['a','b',...])

# boolean args
action='store_true'
action='store_false'

Examples

# positional
parser.add_argument('output-file',
                    help='filepath to save spreadsheet to')

# flag with single argument
parser.add_argument('-s', '--start-date',
                    nargs=1, help='date to start from')

# boolean arguments
parser.add_argument('-v', '--verbose',
                    action='store_true', help='verbose logging')

Argument Properties

parser.add_argument('-p','--filter-projects',
                    default='monday',
                    metavar='MON',    # displayed in help as value
                    type=str)

SubParsers

Sometimes a single CLI interface provides access to a handful of related classes. These classes may take entirely different parameters. In this case, you would implement a subparser for that set of commands.

parser = argparse.ArgumentParser(
      formatter_class = argparse.RawTextHelpFormatter,
      description     = 'A collection of tools for operating on config files',
   )
subparsers = parser.add_subparsers( dest='subparser_name')

## Subparser1 (ModifyKeyVals)
##
modkeyval_parser = subparsers.add_parser( 'ModifyKeyVals', help='Flexible tool to modify configfiles that use the key=value format')

modkeyval_parser.add_argument(
      '-f', '--filepath', help='Path to the configfile we are processing',
      metavar = '/etc/rc.conf',
   )

modkeyval_parser.add_argument(
      '-v', '--verbose', help='Enable detailed logging',
      metavar = '/etc/rc.conf',
   )



## Subparser2 (SSHConfig)
##
sshconfig_parser = subparsers.add_parser( 'SSHConfig', help='modify ~/.ssh/ssh_config "Host" entries. Expects to be run as the user whose ssh_config you are modifying.')

sshconfig_parser.add_argument(
      '-hs', '--host', nargs='+', help='SSH Host value(s)',
      metavar = ['gitbox', '192.168.1.202'],
      )

## Using Variables from SubParsers
##

args = parser.parse_args()
if   args.subparser_name == 'ModifyKeyVals':
	filepath = args.filepath

elif args.subparser_name == 'SSHConfig':
	host     = args.host

python myscript.py ModifyKeyVals -f /path/to/file -v