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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def zPushLens(self, update=None, timeout=None):
 """Copy lens in the Zemax DDE server into LDE"""

        reply = None
        if update == 1:
            reply = self._sendDDEcommand('PushLens,1', timeout)
        elif update == 0 or update is None:
            reply = self._sendDDEcommand('PushLens,0', timeout)
        else:
            raise ValueError('Invalid value for flag')
        if reply:
            return int(reply)   # Note: Zemax returns -999 if push lens fails
        else:
            return -998