The inverse of .join

[Steven D'Aprano]

On Thu, 17 Jun 2010 17:45:41 +0000, Neil Cerutti wrote:

> What's the best way to do the inverse operation of the .join function?

str.join is a many-to-one function, and so it doesn't have an inverse. 
You can't always get the input back unchanged:

>>> L = ["a", "b", "c|d", "e"]
>>> s = '|'.join(L)
>>> s
'a|b|c|d|e'
>>> s.split('|')
['a', 'b', 'c', 'd', 'e']


There's no general way of getting around this -- if split() takes input 
"a|b|c", there is no way even in principle for it to know which of these 
operations it should reverse:

"|".join(["a", "b", "c"])
"|".join(["a|b", "c"])
"|".join(["a", "b|c"])
"|".join(["a|b|c"])
"b".join(["a|", "|c"])

The behaviour with the empty string is just a special case of this.



-- 
Steven