docs: def get_mmcif(code, outfile=None):
      """ Get mmcif file associated with code from PDBE.
  
      Parameters
      ----------
      code : str
          PDB code.
      outfile : str
          Filepath. Writes returned value to this file.
  
      Returns
      -------
      mmcif_file : str
          Filepath to the mmcif file.
      """
      pdbe_url = "http://www.ebi.ac.uk/pdbe/entry-files/download/{0}.cif".format(code)
      r = requests.get(pdbe_url)
      if r.status_code == 200:
          mmcif_string = r.text
      else:
          print("Could not download mmcif file for {0}".format(code))
          mmcif_string = None
  
      # Write to file.
      if outfile and mmcif_string:
          with open(outfile, 'w') as foo:
              foo.write(mmcif_string)
  
      return mmcif_string