code: def extract_db_info(self, obj, keys):
          
  
          objl = self.convert(obj)
  
          result = super(DataFrameType, self).extract_db_info(objl, keys)
          ext = self.datamodel.extractor_map['fits']
          if objl:
              with objl.open() as hdulist:
                  for field in keys:
                      result[field] = ext.extract(field, hdulist)
  
                  tags = result['tags']
                  for field in self.tags_keys:
                      tags[field] = ext.extract(field, hdulist)
  
                  return result
          else:
              return result
docs: Extract tags from serialized file