python中指定分隔符分割字符串，返回三元组

1、

>>> a = "abcabcabcabc"
>>> len(a)
12
>>> a.partition("b")   ## 设定b为分割符，返回三元组
('a', 'b', 'cabcabcabc')
>>> a.partition("x")   ## 字符串中不含有指定分隔符
('abcabcabcabc', '', '')

2、

>>> a = "abcdefgabc"
>>> a.partition("b")
('a', 'b', 'cdefgabc')
>>> a.rpartition("b")
('abcdefga', 'b', 'c')