[Python-Dev] Directions for reproducing the coredump (original) (raw)

Tim Peters tim_one@email.msn.com
Sat, 12 Aug 2000 03:32:17 -0400

[Eric S. Raymond, with a lot of code that dies in a lot of pain]

Eric, as I'm running on a Windows laptop right now, there's not much I can do to try to run this code. However, something struck me in your patch "by eyeball", and here's a self-contained program that crashes under Windows:

This is esr's new class.

class Requirement: "A requirement, together with a message to be shown if it's violated." def init(self, wff, message=None): self.predicate = wff self.message = message

def str(self):
    return display_expression(self.predicate)

def __repr__(self):
    if self.message:
        return self.message
    else:
        return str(self)

This is my driver.

r = Requirement("trust me, I'm a wff!") print r

Could that be related to your problem? I think you really wanted to name "str" as "str" in this class (or if not, comment in extreme detail why you want to confuse the hell out of the reader ). As is, my

print r

attempts to get look up r.str, which isn't found, so Python falls back to using r.repr. That is found, but r.message is None, so Requirement.repr executes

return str(self)

And then we go thru the whole "no str" -> "try repr" -> "message is None" -> "return str(self)" business again, and end up with unbounded recursion. The top of the stacktrace Ping posted does show that the code is failing to find a "str" attr, so that's consistent with the scenario described here.

If this is the problem, note that ways to detect such kinds of unbounded recursion have been discussed here within the last week. You're a clever enough fellow that I have to suspect you concocted this test case as a way to support the more extreme of those proposals without just saying "+1" .