一个是分割，一个是连接。
惯例，先看内部帮助文档
Help on method_descriptor: join(...)
S.join(iterable) -> string Return a string which is the concatenation of the strings in the
iterable. The separator between elements is S.
(END)
将可迭代对象（包含的应该是str类型的，不然会报错）连接起来， 返回值是str，用法如下：
In [2]: s = ['hello', 'world'] In [3]: '_'.join(s)
Out[3]: 'hello_world' In [4]: ''.join(s)
Out[4]: 'helloworld' In [5]: '&&'.join(s)
Out[5]: 'hello&&world' In [6]: '_'.join((1, 2, 3))
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-6-48e56abfc814> in <module>()
----> 1 '_'.join((1, 2, 3)) TypeError: sequence item 0: expected string, int found
再看split函数：
Help on method_descriptor: split(...)
S.split([sep [,maxsplit]]) -> list of strings Return a list of the words in the string S, using sep as the
delimiter string. If maxsplit is given, at most maxsplit
splits are done. If sep is not specified or is None, any
whitespace string is a separator and empty strings are removed
from the result.
(END)
将字符串分割，空格或者空字符都会被移除，返回值是str的列表，第二个参数是分割次数，用法如下：
In [9]: s = 'life is short, I use Python' In [10]: s.spl
s.split s.splitlines In [10]: s.split()
Out[10]: ['life', 'is', 'short,', 'I', 'use', 'Python'] In [11]: s.split(',')
Out[11]: ['life is short', ' I use Python'] In [12]: s.split(',' or '.')
Out[12]: ['life is short', ' I use Python'] In [13]: s.split(',', 3)
Out[13]: ['life is short', ' I use Python'] In [14]: s.split(',', 5)
Out[14]: ['life is short', ' I use Python'] In [15]: s = 'hello, world. Life is short, I use Python' In [16]: s.split(',', 5)
Out[16]: ['hello', ' world. Life is short', ' I use Python'] In [17]: s.split(',', 2)
Out[17]: ['hello', ' world. Life is short', ' I use Python'] In [18]: s.split(',', 1)
Out[18]: ['hello', ' world. Life is short, I use Python'] In [19]: s.split(',' or '.', 2)
Out[19]: ['hello', ' world. Life is short', ' I use Python']