code: def _is_sub_intrinsic(data):
          
          return isinstance(data, dict) and len(data) == 1 and LambdaUri._FN_SUB in data
docs: Is this input data a Fn::Sub intrinsic function
  
          Parameters
          ----------
          data
              Data to check
  
          Returns
          -------
          bool
              True if the data Fn::Sub intrinsic function