I was just looking at a thread on here where I saw this answer. I tried it on my python 3 compiler, but for some reason it didn't work. And in the official python documentation for regex I can't seem to find anything for {e<=1}. Did it get removed or replaced?
For reference, here is the code and its output:
>>> import re
>>> m = re.findall("(AA){e<=1}", "CAAG")
>>> m
[]