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
Type "help", "copyright", "credits" or "license()" for more information.
>>> # 可变集合
>>> s = set([1,2,3,4])
>>> s
{1, 2, 3, 4}
>>> s.add(5)
>>> s
{1, 2, 3, 4, 5}
>>> 
>>> 
>>> # 不可变集合
>>> fs = frozenset([0,1,2,3,4])
>>> fs
frozenset({0, 1, 2, 3, 4})
>>> fs.add(5)
Traceback (most recent call last):
  File "<pyshell#10>", line 1, in <module>
    fs.add(5)
AttributeError: 'frozenset' object has no attribute 'add'
>>> 
>>> 
>>> set("Happy")
{'a', 'p', 'H', 'y'}
>>> 
>>> frozenset("Happy")
frozenset({'a', 'p', 'H', 'y'})
>>> 
>>>