Suppose you want to build a tool with a simple interface:
usage: sub <command>Python proposes to use argparse module. And if you follow documentation, the best you can get will be this output:
commands:
status - show status
list - print list
usage: sub {status,list} ...
positional arguments:
{status,list}
status show status
list print list
And it you implement proper formatting, your code will look like this:
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())
Here you may see the failure of OOP (object oriented programming). The proper answer to this formatting problem is just to define a data structure for command line help in JSON or similar format and let people dump and process it with templates. Once option definition is parsed, the information there is static, so there is no need in those intertwined recursive method calls. So just do it in 2 pass - get dataset and render template.