    """
    DateInterval.py

    Convert interval strings (in the form of 1w2d, etc) to
    seconds, and back again.  Is not exactly about months or
    years (leap years in particular).

    Accepts (y)ear, (b)month, (w)eek, (d)ay, (h)our, (m)inute, (s)econd.

    Exports only timeEncode and timeDecode functions.
    """

    import re

    second = 1
    minute = second*60
    hour = minute*60
    day = hour*24
    week = day*7
    month = day*30
    year = day*365
    timeValues = {
        'y': year,
        'b': month,
        'w': week,
        'd': day,
        'h': hour,
        'm': minute,
        's': second,
        }
    timeOrdered = timeValues.items()
    timeOrdered.sort(lambda a, b: -cmp(a[1], b[1]))

    def timeEncode(seconds):
        """Encodes a number of seconds (representing a time interval)
        into a form like 1h2d3s."""
        s = ''
        for char, amount in timeOrdered:
            if seconds >= amount:
                i, seconds = divmod(seconds, amount)
                s += '%i%s' % (i, char)
        return s

    _timeRE = re.compile(r'[0-9]+[a-zA-Z]')
    def timeDecode(s):
        """Decodes a number in the format 1h4d3m (1 hour, 3 days, 3 minutes)
        into a number of seconds"""
        time = 0
        for match in allMatches(s, _timeRE):
            char = match.group(0)[-1].lower()
            if not timeValues.has_key(char):
                # @@: should signal error
                continue
            time += int(match.group(0)[:-1]) * timeValues[char]
        return time

    # @@-sgd 2002-12-23 - this function does not belong in this module, find a better place.
    def allMatches(source, regex):
        """Return a list of matches for regex in source
        """
        pos = 0
        end = len(source)
        rv = []
        match = regex.search(source, pos)
        while match:
            rv.append(match)
            match = regex.search(source, match.end() )
        return rv

    __all__ = [timeEncode, timeDecode]