argparse_range.py

class Range(object):
    """Represents an integer range"""

    regex = re.compile(r'(?P<low>\d+|-\d+)?\.\.(?P<high>\d+|-\d+)')

    def __init__(self, low, high):
        self.low = low
        self.high = high

    def __repr__(self):
        return '<Range {0}..{1}>'.format(self.low, self.high)

    @classmethod
    def from_argparse(cls, value):
        """Helper for argparse that accepts strings like
            low..high
            ..high
        where `low` and `high` are (possibly negative) integers. If `low` is omitted it defaults to 0.
        `low` must always be smaller than `high`.
        """

        match = cls.regex.match(value)
        if match is None:
            raise argparse.ArgumentTypeError('{0} is no a valid range'.format(value))

        low = match.group('low')
        if low is None:
            low = 0
        else:
            low = int(low)
        high = int(match.group('high'))

        if low > high:
            raise argparse.ArgumentTypeError('low value cannot be greater than high value')

        return cls(low=int(low), high=int(high))