hms_time.py

import re


_RE_HMS = re.compile(
    r'^\s*(?:(?P<h>\d+)h)?\s*(?:(?P<m>\d+)m)?\s*(?:(?P<s>\d+)s?)?\s*$')


def to_hms(seconds):
    """Converts seconds (int) to "h m s" (str)."""
    minutes, seconds = divmod(seconds, 60)
    hours, minutes = divmod(minutes, 60)
    _format = ''
    if seconds:
        _format = '{seconds}s'
    if minutes:
        _format = '{minutes}m' + (' ' + _format if _format else _format)
    if hours:
        _format = '{hours}h' + (' ' + _format if _format else _format)
    return _format.format(hours=hours, minutes=minutes, seconds=seconds)


def from_hms(hms_string):
    """Converts "h m s" (str) to seconds (int)."""
    match_hms = _RE_HMS.match(str(hms_string))
    if not match_hms:
        raise ValueError('"{}" is not a valid time!'.format(hms_string))
    hms_multipliers = {k: int(match_hms.group(k))
                       if match_hms.group(k) is not None else 0
                       for k in 'hms'}
    return (hms_multipliers['h'] * 3600 +
            hms_multipliers['m'] * 60 +
            hms_multipliers['s'])