Could you include the rest of the cases that LCatro was mentioning? He mentioned another 2 for lists.

@pablogsal

poc3 is not reproducible on my local mac machine and Linux machine.
However poc2 is reproducible, so I will add the patch on this PR.

$ cat poc3.py
class poc() :
    def __eq__(self,other) :
        list1.clear()
        return NotImplemented

list1 = [ set() ]
poc() in list1
print('end')

$ ./python poc3.py
end

FWIW, LCatro had opened another issue (https://bugs.python.org/issue38610) for similar crashes in the index(), count(), and remove() methods of list. I had created GH-17022 to address them.