def valid_beat_duration(duration):
    """Return True when log2(duration) is an integer."""
    if duration == 0:
        return False
    elif duration == 1:
        return True
    else:
        r = duration
        while r != 1:
            if r % 2 == 1:
                return False
            r /= 2
        return True
Return True when log2(duration) is an integer.