Can someone please point out why do we have to do that dance with recursion limit?

I've came upon this problem as well. I had some (bad) API I had to work with. It always raised the same exception with the only difference in the message. So I thought I could do something like this:

def message_contains(msg):
    class _MyExc(object):
        def __instancecheck__(self, exc):
            return msg in exc.args[0]
    return _MyExc

But after I tried it in number of different ways I found out that it's not possible.

So here's another reason to change this behavior.