Fastest Python method for search and replace on a large string

Question

I\'m looking for the fastest way to replace a large number of sub-strings inside a very large string. Here are two examples I\'ve used.

findall() feels simpler and

Answer 1

The standard method is to use the built-in

re.sub(reg, rep, text)

Incidentally the reason for the performance difference between your versions is that each replacement in your first version causes the entire string to be recopied. Copies are fast, but when you're copying 10 MB at a go, enough copies will become slow.