code: def add_variable(variable, var_list):
      """Adds variable to a given list.
  
      Args:
          variable: A (list of) variable(s).
          var_list (list): The list where the :attr:`variable` are added to.
      """
      if isinstance(variable, (list, tuple)):
          for var in variable:
              add_variable(var, var_list)
      else:
          if variable not in var_list:
              var_list.append(variable)
  
imports: import tensorflow
label_desc: Use image node_id 2 for calling a global function with example usage: add_variable(variable, var_list) without return types