Python argparse value range help message appearance

Question

I have an argument for a program that is an integer from 1-100 and I just don\'t like the way that it shows up in the -h help message when using argparse (it literally lists 0,

Answer 1

With a custom type, it is easier to control the error message (via the ArgumentTypeError). I still need the metavar to control the usage display.

import argparse

def range_type(astr, min=0, max=101):
    value = int(astr)
    if min<= value <= max:
        return value
    else:
        raise argparse.ArgumentTypeError('value not in range %s-%s'%(min,max))

parser = argparse.ArgumentParser()
norse = parser.add_argument_group('Norse')
...
norse.add_argument('--range', type=range_type, 
    help='Value in range: Default is %(default)s.',
    default=49, metavar='[0-101]')
parser.print_help()
print parser.parse_args()

producing:

2244:~/mypy$ python2.7 stack25295487.py --ran 102
usage: stack25295487.py [-h] [-n] [--threshold [0:101]] [--range [0-101]]

optional arguments:
  -h, --help           show this help message and exit

Norse:
  ...
  --range [0-101]      Value in range: Default is 49.
usage: stack25295487.py [-h] [-n] [--threshold [0:101]] [--range [0-101]]
stack25295487.py: error: argument --range: value not in range 0-101

I could use functools.partial to customize the range values:

type=partial(range_type, min=10, max=90)