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
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