Python 中 list 没有 add 属性

 1>>> A = (['a', 'b', 'c', 'd'])
 2>>> 'a' in A
 3True
 4>>> 'e' in A
 5False
 6>>> ABC = A.copy()
 7>>> ABC.add('e')
 8Traceback (most recent call last):
 9  File "<stdin>", line 1, in <module>
10AttributeError: 'list' object has no attribute 'add'
11# no exit() 仍然报属性错误
12>>> abc = A.copy()
13>>> abc.add('e')
14Traceback (most recent call last):
15  File "<stdin>", line 1, in <module>
16AttributeError: 'list' object has no attribute 'add'
17>>>

 1>>> abc = set(['a', 'b', 'c', 'd'])
 2>>> 'a' in abc
 3True
 4>>> 'e' in abc
 5False
 6>>> abcd = abc.copy()
 7>>> abcd.add('e')
 8>>> abcd.issuperset(abc)
 9True
10>>> abc.remove('c')
11>>> abc & abcd #  或者是 abc.intersection(abcd)
12{'d', 'a', 'b'}
13>>>