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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.