Compress a list of integers into a list of ranges. For example, `1 2 3 4 5 7 8 9` becomes `1:6 7:10`. The code can be used both as a library and as an executable.

nums2ranges.py

#!/usr/bin/env python3


def nums2ranges(nums):
    """
    >>> list(nums2ranges([]))
    []
    >>> list(nums2ranges([0, 1, 2, 3, 4]))
    [slice(0, 5, None)]
    >>> list(nums2ranges([0, 1, 4, 5, 6]))
    [slice(0, 2, None), slice(4, 7, None)]
    >>> list(nums2ranges([0, 2, 7, 9, 10, 13]))
    [slice(0, 1, None), slice(2, 3, None), slice(7, 8, None), slice(9, 11, None), slice(13, 14, None)]
    >>> list(nums2ranges([0, 0, 0]))
    [slice(0, 1, None), slice(0, 1, None), slice(0, 1, None)]
    >>> list(nums2ranges([0, 1, 2, 1, 2, 3]))
    [slice(0, 3, None), slice(1, 4, None)]
    """
    start = None
    stop = None
    counter = None
    for x in nums:
        if start is None:
            start = x
            counter = 0
            stop = x + 1
        elif x - start == counter:
            stop = x + 1
        else:
            yield slice(start, stop)
            start = x
            counter = 0
            stop = x + 1
        counter += 1
    if start is not None:
        yield slice(start, stop)


if __name__ == '__main__':
    import argparse
    import sys

    def make_parser():
        parser = argparse.ArgumentParser(
            description=('Convert integers to ranges. For example, given '
                         'numbers 1, 2, 3, 6, 7, 10, 0, 1, '
                         'ranges 1:4, 6:8, 10:11, 0:2 '
                         'will be printed. Numbers are expected from stdin '
                         'one per line. Ranges are printed to stdout one per '
                         'line.'),
            epilog=('Return code: 0) success; 1) non-integer line occurred '
                    'when in strict mode (see --strict flag); 130) when '
                    'aborted by Ctrl-c'))
        parser.add_argument(
            '-s',
            '--strict',
            action='store_true',
            help=('by default non-integer lines will be omitted; using this '
                  'flag aborts and raises error upon invalid line'))
        parser.add_argument(
            '-i',
            '--inclusive',
            action='store_true',
            help=('making the second token of a range (a.k.a. the stop), '
                  'inclusive'))
        return parser

    def parse_ints(lines, strict):
        for l in map(str.strip, lines):
            try:
                x = int(l)
            except ValueError:
                if strict:
                    raise
            else:
                yield x

    def main():
        args = make_parser().parse_args()
        try:
            if args.inclusive:
                for sl in nums2ranges(parse_ints(sys.stdin, args.strict)):
                    print('{}:{}'.format(sl.start, sl.stop - 1))
            else:
                for sl in nums2ranges(parse_ints(sys.stdin, args.strict)):
                    print('{}:{}'.format(sl.start, sl.stop))
        except ValueError as err:
            print(err, file=sys.stderr)
            return 1
        except BrokenPipeError:
            sys.stderr.close()
            return 130
        except KeyboardInterrupt:
            return 130
        return 0

    sys.exit(main())