使用元组代替列表。元组是不可变的，可以用作字典键：

Use a tuple in place of the list. Tuples are immutable and can be used as dictionary keys:

d[(attrib_a, attrib_b)] = t

括号可以省略：

d[attrib_a, attrib_b] = t

然而，有些人似乎不喜欢这种语法。

However, some people seem to dislike this syntax.