code: def _get_variable_value(defined_variables, name):
      
      def fallback(*args, **kwargs):
          raise AssertionError("Variable {0} is not defined in class {1}".format(
                  name, defined_variables.__class__.__name__))
      method = getattr(defined_variables, name, fallback)
      val = method()
      return method.field_type(val)
docs: Call the function provided on the defined_variables object with the
      given name (raise exception if that doesn't exist) and casts it to the
      specified type.
  
      Returns an instance of operators.BaseType