In the re module, re._compile gets called when using most re methods.
In my use case (which I think is not rare) I have a small number of compiled patterns that I have to match against a large number of short strings

profiling showed that half of the total runtime was still spent in re._compile, checking for the type of the flags and trying to get the pattern in a cache

Example code that exhibits this behavior:

import re

pattern = re.compile("spam")
string = "Monty pythons"
for _ in range(1000000):
    re.search(pattern, string)