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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 _init_lazy_fields(self):
 """ Member data that gets loaded or constructed on demand """

        self.gtf_path = None
        self._protein_sequences = None
        self._transcript_sequences = None
        self._db = None
        self.protein_fasta_paths = None
        self.transcript_fasta_paths = None

        # only memoizing the Gene, Transcript, and Exon objects
        self._genes = {}
        self._transcripts = {}
        self._exons = {}