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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 __set_output(self):
 """ Private method to set the file to write the cache to. Automaticaly set once the ifo, start and end times have been set. """

    if self.__start and self.__end and self.__observatory and self.__type:
      self.__output = os.path.join(self.__job.get_cache_dir(), self.__observatory + '-' + self.__type +'_CACHE' + '-' + str(self.__start) + '-' + str(self.__end - self.__start) + '.lcf')
      self.set_output(self.__output)