code: def urls(self, key, value):
      
      def _is_preprint(value):
          return value.get('y', '').lower() == 'preprint'
  
      def _is_fulltext(value):
          return value['u'].endswith('.pdf') and value['u'].startswith('http://cds.cern.ch')
  
      def _is_local_copy(value):
          return 'local copy' in value.get('y', '')
  
      def _is_ignored_domain(value):
          ignored_domains = ['http://cdsweb.cern.ch', 'http://cms.cern.ch',
                             'http://cmsdoc.cern.ch', 'http://documents.cern.ch',
                             'http://preprints.cern.ch', 'http://cds.cern.ch',
                             'http://arxiv.org']
          return any(value['u'].startswith(domain) for domain in ignored_domains)
  
      field_8564 = self.get('8564_', [])
      field_FFT = self.get('FFT__', [])
  
      if 'u' not in value:
          return field_8564
  
      url = escape_url(value['u'])
  
      if _is_fulltext(value) and not _is_preprint(value):
          if _is_local_copy(value):
              description = value.get('y', '').replace('local copy', 'on CERN Document Server')
              field_8564.append({
                  'u': url,
                  'y': description,
              })
          else:
              _, file_name = os.path.split(urllib.parse.urlparse(value['u']).path)
              _, extension = os.path.splitext(file_name)
              field_FFT.append({
                  't': 'CDS',
                  'a': url,
                  'd': value.get('y', ''),
                  'n': file_name,
                  'f': extension,
              })
      elif not _is_ignored_domain(value):
          field_8564.append({
              'u': url,
              'y': value.get('y'),
          })
  
      self['FFT__'] = field_FFT
      return field_8564
docs: Populate the ``8564`` MARC field.
  
      Also populate the ``FFT`` field through side effects.