code: def key_value(self, **kwargs):
          
          field_name = self.name
          new_df = copy_df(self)
          new_df._perform_operation(op.FieldKVConfigOperation({field_name: KVConfig(**kwargs)}))
          return new_df
docs: Set fields to be key-value represented.
  
          :rtype: Column
  
          :Example:
  
          >>> new_ds = df.key_value('f1 f2', kv=':', item=',')