code: def create_variable_with_length(self):
          
          variable_name = '{}_len'.format(self._variable)
          if variable_name in self._variables:
              return
          self._variables.add(variable_name)
          self.l('{variable}_len = len({variable})')
docs: Append code for creating variable with length of that variable
          (for example length of list or dictionary) with name ``{variable}_len``.
          It can be called several times and always it's done only when that variable
          still does not exists.