How about an operator, then?
We already have % rather than a string.format or some such. Presumably this is because Guido thought it was such a handy thing that it should be instantly available at our fingertips. I think a similar argument could be made for string.join, and also its inverse string.split.
So, how about:
x & s == string.join(x, s)
s1 | s2 == string.split(s1, s2)
I don't see the mnemonic. (For %, the mnemonic is clear: %s, %d etc.)
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)