Python Language CLI subcommands with precise help output
Introduction
Different ways to create subcommands like in hg or svn with the exact command line interface and help output as shown in Remarks section.
Parsing Command Line arguments covers broader topic of arguments parsing.
Remarks
Different ways to create subcommands like in hg or svn with the command line interface shown in the help message:
usage: sub <command>
commands:
status - show status
list - print list
Native way (no libraries)
"""
usage: sub <command>
commands:
status - show status
list - print list
"""
import sys
def check():
print("status")
return 0
if sys.argv[1:] == ['status']:
sys.exit(check())
elif sys.argv[1:] == ['list']:
print("list")
else:
print(__doc__.strip())
Output without arguments:
usage: sub <command>
commands:
status - show status
list - print list
Pros:
- no deps
- everybody should be able to read that
- complete control over help formatting
argparse (default help formatter)
import argparse
import sys
def check():
print("status")
return 0
parser = argparse.ArgumentParser(prog="sub", add_help=False)
subparser = parser.add_subparsers(dest="cmd")
subparser.add_parser('status', help='show status')
subparser.add_parser('list', help='print list')
# hack to show help when no arguments supplied
if len(sys.argv) == 1:
parser.print_help()
sys.exit(0)
args = parser.parse_args()
if args.cmd == 'list':
print('list')
elif args.cmd == 'status':
sys.exit(check())
Output without arguments:
usage: sub {status,list} ...
positional arguments:
{status,list}
status show status
list print list
Pros:
- comes with Python
- option parsing is included
argparse (custom help formatter)
Extended version of http://www.riptutorial.com/python/example/25282/argparse--default-help-formatter- that fixed help output.
import argparse
import sys
class CustomHelpFormatter(argparse.HelpFormatter):
def _format_action(self, action):
if type(action) == argparse._SubParsersAction:
# inject new class variable for subcommand formatting
subactions = action._get_subactions()
invocations = [self._format_action_invocation(a) for a in subactions]
self._subcommand_max_length = max(len(i) for i in invocations)
if type(action) == argparse._SubParsersAction._ChoicesPseudoAction:
# format subcommand help line
subcommand = self._format_action_invocation(action) # type: str
width = self._subcommand_max_length
help_text = ""
if action.help:
help_text = self._expand_help(action)
return " {:{width}} - {}\n".format(subcommand, help_text, width=width)
elif type(action) == argparse._SubParsersAction:
# process subcommand help section
msg = '\n'
for subaction in action._get_subactions():
msg += self._format_action(subaction)
return msg
else:
return super(CustomHelpFormatter, self)._format_action(action)
def check():
print("status")
return 0
parser = argparse.ArgumentParser(usage="sub <command>", add_help=False,
formatter_class=CustomHelpFormatter)
subparser = parser.add_subparsers(dest="cmd")
subparser.add_parser('status', help='show status')
subparser.add_parser('list', help='print list')
# custom help messge
parser._positionals.title = "commands"
# hack to show help when no arguments supplied
if len(sys.argv) == 1:
parser.print_help()
sys.exit(0)
args = parser.parse_args()
if args.cmd == 'list':
print('list')
elif args.cmd == 'status':
sys.exit(check())
Output without arguments:
usage: sub <command>
commands:
status - show status
list - print list
