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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_document_list(self):
 """ Retrieves all documents included in this project. """

        try:
            return self.__dict__['document_list']
        except KeyError:
            obj_list = DocumentSet([
                self._connection.documents.get(i) for i in self.document_ids
            ])
            self.__dict__['document_list'] = obj_list
            return obj_list