join() is a string method and while using it the separator string iterates over an arbitrary sequence, forming string representations of each of the elements, inserting itself between the elements.

join()是一个字符串方法，使用它时，分隔符字符串会在任意序列上迭代，从而形成每个元素的字符串表示形式，并在元素之间插入自己。

Concisely, it's because join and string.join() are both generic operations that work on any iterable and is a string method.

简而言之，这是因为join和string.join()都是可在任何可迭代对象上使用的通用操作，并且是字符串方法。

Because it is a string method, the join() can work for the Unicode string as well as plain ASCII strings.

因为它是一个字符串方法，所以join()可以用于Unicode字符串以及普通ASCII字符串。

Example Usage of string.join(list)

示例string.join(list)的用法

-bash-4.2$ python3
Python 3.6.8 (default, Apr 25 2019, 21:02:35)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> test_string = "test"
>>> test_string.join("1234")
'1test2test3test4'
>>>

In the above example, the string "test" is joined with every character provided as a join argument.

在上面的示例中，字符串“ test”与作为连接参数提供的每个字符连接在一起。

-bash-4.2$ python3
Python 3.6.8 (default, Apr 25 2019, 21:02:35)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> test_string = "test"
>>> test_string.join("---")
'-test-test-'
>>>

翻译自: https://www.includehelp.com/python/why-is-it-string-join-list-instead-of-list-join-string.aspx