Update self and parent with intermediate progress.

def update(self, sent):
        """ Update self and parent with intermediate progress. """
        self.offset = sent

        now = datetime.datetime.now()

        elapsed = (now - self.startTime).total_seconds()
        if elapsed > 0:
            mbps = (sent * 8 / (10 ** 6)) / elapsed
        else:
            mbps = None

        self._display(sent, now, self.name, mbps)