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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 zLoadFile(self, fileName, append=None):
 """Loads a zmx file into the DDE server"""

        reply = None
        if append:
            cmd = "LoadFile,{},{}".format(fileName, append)
        else:
            cmd = "LoadFile,{}".format(fileName)
        reply = self._sendDDEcommand(cmd)
        if reply:
            return int(reply) #Note: Zemax returns -999 if update fails.
        else:
            return -998