code: def compute_optional_conf(conf_name, default_value, **all_config):
      
      conf_value = all_config.get(conf_name)
      if conf_value is not None:
          # Validate configuration value.
          conf_value = get_validator(conf_name)(conf_value)
      else:
          conf_value = default_value
      return conf_value
docs: Returns *conf_name* settings if provided in *all_config*, else returns
       *default_value*.
  
      Validates *conf_name* value if provided.