def timedelta(string):
    """
    Parse :param string: into :class:`datetime.timedelta`, you can use any
    (logical) combination of Nw, Nd, Nh and Nm, e.g. `1h30m` for 1 hour, 30
    minutes or `3w` for 3 weeks.

    Raises a ValueError if the input is invalid/unparseable.

    >>> print(timedelta("3w"))
    21 days, 0:00:00
    >>> print(timedelta("3w 12h 57m"))
    21 days, 12:57:00
    >>> print(timedelta("1h30m37s"))
    1:30:37
    >>> print(timedelta("1asdf3w"))
    Traceback (most recent call last):
        ...
    ValueError: invalid human-readable timedelta
    """

    keys = ["weeks", "days", "hours", "minutes", "seconds"]
    regex = "".join(["((?P<%s>\\d+)%s ?)?" % (k, k[0]) for k in keys])
    kwargs = {}
    for k, v in re.match(regex, string).groupdict(default="0").items():
        kwargs[k] = int(v)

    rv = datetime.timedelta(**kwargs)
    if rv == datetime.timedelta():
        raise ValueError("invalid human-readable timedelta")

    return datetime.timedelta(**kwargs)