code: def create_variable_is_list(self):
          
          variable_name = '{}_is_list'.format(self._variable)
          if variable_name in self._variables:
              return
          self._variables.add(variable_name)
          self.l('{variable}_is_list = isinstance({variable}, list)')
docs: Append code for creating variable with bool if it's instance of list
          with a name ``{variable}_is_list``. Similar to `create_variable_with_length`.