docs: def _prepare_imports(self, dicts):
  
          """ filters the import stream to remove duplicates
  
          also serves as a good place to override if anything special has to be done to the
          order of the import stream (see OrganizationImporter)
          """
          # hash(json): id
          seen_hashes = {}
  
          for data in dicts:
              json_id = data.pop('_id')
  
              # map duplicates (using omnihash to tell if json dicts are identical-ish)
              objhash = omnihash(data)
              if objhash not in seen_hashes:
                  seen_hashes[objhash] = json_id
                  yield json_id, data
              else:
                  self.duplicates[json_id] = seen_hashes[objhash]