I use the following simple code to parse some arguments; note that one of them is required. Unfortunately, when the user runs the script without providing the argument, the displayed usage/help text does not indicate that there is a non-optional argument, which I find very confusing. How can I get python to indicate that an argument is not optional?
Here is the code:
import argparse
if __name__ == '__main__':
parser = argparse.ArgumentParser(
description='Foo')
parser.add_argument('-i','--input', help='Input file name', required=True)
parser.add_argument('-o','--output', help='Output file name', default="stdout")
args = parser.parse_args()
print ("Input file: %s" % args.input )
print ("Output file: %s" % args.output )
When running above code without providing the required argument, I get the following output:
usage: foo.py [-h] -i INPUT [-o OUTPUT]
Foo
optional arguments:
-h, --help show this help message and exit
-i INPUT, --input INPUT
Input file name
-o OUTPUT, --output OUTPUT
Output file name
Building off of @Karl Rosaen
parser = argparse.ArgumentParser()
optional = parser._action_groups.pop() # Edited this line
required = parser.add_argument_group('required arguments')
# remove this line: optional = parser...
required.add_argument('--required_arg', required=True)
optional.add_argument('--optional_arg')
parser._action_groups.append(optional) # added this line
return parser.parse_args()
and this outputs:
usage: main.py [-h] [--required_arg REQUIRED_ARG]
[--optional_arg OPTIONAL_ARG]
required arguments:
--required_arg REQUIRED_ARG
optional arguments:
-h, --help show this help message and exit
--optional_arg OPTIONAL_ARG
Since I prefer to list required arguments before optional, I hack around it via:
parser = argparse.ArgumentParser()
parser._action_groups.pop()
required = parser.add_argument_group('required arguments')
optional = parser.add_argument_group('optional arguments')
required.add_argument('--required_arg', required=True)
optional.add_argument('--optional_arg')
return parser.parse_args()
and this outputs:
usage: main.py [-h] [--required_arg REQUIRED_ARG]
[--optional_arg OPTIONAL_ARG]
required arguments:
--required_arg REQUIRED_ARG
optional arguments:
--optional_arg OPTIONAL_ARG
I can live without 'help' showing up in the optional arguments group.
One more time, building off of @RalphyZ
This one doesn't break the exposed API.
from argparse import ArgumentParser, SUPPRESS
# Disable default help
parser = ArgumentParser(add_help=False)
required = parser.add_argument_group('required arguments')
optional = parser.add_argument_group('optional arguments')
# Add back help
optional.add_argument(
'-h',
'--help',
action='help',
default=SUPPRESS,
help='show this help message and exit'
)
required.add_argument('--required_arg', required=True)
optional.add_argument('--optional_arg')
Which will show the same as above and should survive future versions:
usage: main.py [-h] [--required_arg REQUIRED_ARG]
[--optional_arg OPTIONAL_ARG]
required arguments:
--required_arg REQUIRED_ARG
optional arguments:
-h, --help show this help message and exit
--optional_arg OPTIONAL_ARG
Source: Stackoverflow.com