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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 fetch_pdb(self, pdb_code):
 """Fetches PDB file contents from the Protein Databank at rcsb.org. Parameters pdb_code : str A 4-letter PDB code, e.g., "3eiy". Returns --------- self """

        self.pdb_path, self.pdb_text = self._fetch_pdb(pdb_code)
        self._df = self._construct_df(pdb_lines=self.pdb_text.splitlines(True))
        return self