code: def finish(cls, document):
          
          target_document = {}
          document_copy = {}
          for field_name, value in document.items():
              maker = cls._instructions[field_name]
              target_document = document.copy()
              with maker.target(target_document):
                  document_copy[field_name] = maker(value)
                  target_document[field_name] = document_copy[field_name]
          return document_copy
docs: Take a assembled document and convert all assembled values to
          finished values.