from string to list to string.

[snippsat]

str.join() is faster than replace()... I think

Replace is faster,there is 1 more function call in(join() + split()).
About 3-sec faster in a 10000000 timeit loop.

Now do this not matter all for this task,
and his last requirement destroy it for replace() 

would I get an output of John Doe, 56 from John Doe 56?

That's why i did hint about rsplit().