code: def _desy_bookkeeping2marc(self, key, value):
      
      if 'identifier' not in value:
          return {
              'a': value.get('expert'),
              'd': value.get('date'),
              's': value.get('status'),
          }
  
      self.setdefault('035', []).append({
          '9': 'DESY',
          'z': value['identifier']
      })
docs: Populate the ``595_D`` MARC field.
  
      Also populates the ``035`` MARC field through side effects.