Python frozenset

用法：frozenset([iterable])

定义：返回一个冻结的集合，冻结后的集合不能添加或删除函数

示例：

>>> list = ['a','b','c','d','e','f','a','b','c'] >>> print(len(list),list)9 ['a', 'b', 'c', 'd', 'e', 'f', 'a', 'b', 'c']>>> set = frozenset(list)>>> print(len(set),set)6 frozenset({'a', 'b', 'c', 'e', 'd', 'f'})>>> set.add('g')Traceback (most recent call last):  File "<stdin>", line 1, in <module>AttributeError: 'frozenset' object has no attribute 'add'