code: def merge_setting(request_setting, session_setting, dict_class=OrderedDict):
      
  
      if session_setting is None:
          return request_setting
  
      if request_setting is None:
          return session_setting
  
      # Bypass if not a dictionary (e.g. verify)
      if not (
              isinstance(session_setting, Mapping) and
              isinstance(request_setting, Mapping)
      ):
          return request_setting
  
      merged_setting = dict_class(to_key_val_list(session_setting))
      merged_setting.update(to_key_val_list(request_setting))
  
      # Remove keys that are set to None.
      for (k, v) in request_setting.items():
          if v is None:
              del merged_setting[k]
  
      merged_setting = dict((k, v) for (k, v) in merged_setting.items() if v is not None)
  
      return merged_setting
docs: Determines appropriate setting for a given request, taking into account the
      explicit setting on that request, and the setting in the session. If a
      setting is a dictionary, they will be merged together using `dict_class`