Thank you for the 'positive lookbehind assertion' for anchoring the match after '('. That is what I was missing. '[^,]' is too broad as, in particular, it matches the ')' in 'a(self)'. We don't want the ')' removed. The tests passed with a faulty re because the method test was faulty in that it only tested that something is removed, but not that the removal is correct. I fixed the tests also to really test proper removal.