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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 get_fields(self):
 """ Returns used fields of model """

        result = [key for key in self.__original_data__.keys()
                  if key not in self.__deleted_fields__]
        result.extend([key for key in self.__modified_data__.keys()
                       if key not in result and key not in self.__deleted_fields__])

        return result