Offset time (in milliseconds) from a |datetime.datetime| object to now

def milliseconds_offset(cls, timestamp, now=None):
        """ Offset time (in milliseconds) from a |datetime.datetime| object to now """
        if isinstance(timestamp, (int, float)):
            base = timestamp
        else:
            base = cls.to_unix(timestamp)
            base += (timestamp.microsecond / 1000000)
        if now is None:
            now = time.time()
        return (now - base) * 1000