Python中可变集合set与不可变集合frozenset

class frozenset([iterable])

代码实验展示:

Python 3.7.4 (tags/v3.7.4:e09359112e, Jul 8 2019, 20:34:20) [MSC v.1916 64 bit (AMD64)] on win32
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 # 可变集合
 s set([1,2,3,4])
{1, 2, 3, 4}
 s.add(5)
{1, 2, 3, 4, 5}