Argparse: Way to include default values in '--help'?
Use the argparse.ArgumentDefaultsHelpFormatter
formatter:
parser = argparse.ArgumentParser( # ... other options ... formatter_class=argparse.ArgumentDefaultsHelpFormatter)
To quote the documentation:
The other formatter class available,
ArgumentDefaultsHelpFormatter
, will add information about the default value of each of the arguments.
Note that this only applies to arguments that have help text defined; with no help
value for an argument, there is no help message to add information about the default value to.
The exact output for your scan-time option then becomes:
--scan-time [SCAN_TIME] Wait SCAN-TIME seconds between status checks. (default: 5)
Add '%(default)s'
to the help parameter to control what is displayed.
parser.add_argument("--type", default="toto", choices=["toto","titi"], help = "type (default: %(default)s)")
Notes:
- It is
%
+ default in parenthesis + format characters (not to be confused with curly brackets{default}
we find informat
or f-string) - Don't forget to add the "specifier character" for the type representation at the end (i.e.
s
for strings,d
for integers,f
for floats, etc.) - You can also add the usual "printf" format specifiers (like number of digits for floats, leading zeros, etc.)
You can refer to printf documentation for more details.
Wrapper class
This is the most reliable and DRY approach I've found so far to both show defaults and use another formatter such as argparse.RawTextHelpFormatter
at the same time:
#!/usr/bin/env python3import argparseclass ArgumentParserWithDefaults(argparse.ArgumentParser): def add_argument(self, *args, help=None, default=None, **kwargs): if help is not None: kwargs['help'] = help if default is not None and args[0] != '-h': kwargs['default'] = default if help is not None: kwargs['help'] += ' Default: {}'.format(default) super().add_argument(*args, **kwargs)parser = ArgumentParserWithDefaults( formatter_class=argparse.RawTextHelpFormatter)parser.add_argument('-a', default=13, help='''my helpfor a''')parser.add_argument('-b', default=42, help='''my helpfor b''')parser.add_argument('--no-default', help='''my helpfor no-default''')parser.add_argument('--no-help', default=101)parser.print_help()print()print(parser.parse_args())
Output:
usage: main.py [-h] [-a A] [-b B] [--no-default NO_DEFAULT] [--no-help NO_HELP]optional arguments: -h, --help show this help message and exit -a A my help for a Default: 13 -b B my help for b Default: 42 --no-default NO_DEFAULT my help for no-default --no-help NO_HELPNamespace(a=13, b=42, no_default=None, no_help=101)
ArgumentDefaultsHelpFormatter
+ RawTextHelpFormatter
multiple inheritance
Multiple inheritance just works, but it does not seem to be public API:
#!/usr/bin/env python3import argparseclass RawTextArgumentDefaultsHelpFormatter( argparse.ArgumentDefaultsHelpFormatter, argparse.RawTextHelpFormatter ): passparser = argparse.ArgumentParser( formatter_class=RawTextArgumentDefaultsHelpFormatter)parser.add_argument('-a', default=13, help='''my helpfor a''')parser.add_argument('-b', default=42, help='''my helpfor b''')parser.print_help()
Output:
usage: a.py [-h] [-a A] [-b B]optional arguments: -h, --help show this help message and exit -a A my help for a (default: 13) -b B my help for b (default: 42)
It just works works because as we can see trivially from the sources https://github.com/python/cpython/blob/v3.6.5/Lib/argparse.py#L648 that:
RawTextHelpFormatter
implements_split_lines
ArgumentDefaultsHelpFormatter
implements_get_help_string
so we can guess that they will work together just fine.
However, this does not seem to be public API, and neither are the methods of formatter_class
, so I don't think there is a public API way to do it currently. argparse
docstring says:
All other classes in this module are considered implementation details. (Also note that HelpFormatter and RawDescriptionHelpFormatter are only considered public as object names -- the API of the formatter objects is still considered an implementation detail.)
See also: Customize argparse help message
Tested on Python 3.6.5.