[Python-Dev] 'with' __exit__ doesn't set sys.exc_info()

Mike Stall jmstall at exchange.microsoft.com
Tue Dec 18 19:11:01 CET 2007


Can somebody confirm the following behavior is expected: When a 'with' statement invokes __exit__(), it looks like sys.exc_info() is not actually set.

I know this may be a very pedantic detail,  but I'm working on IronPython and would like to make it consistent with CPython's behavior.

The PEP (http://www.python.org/dev/peps/pep-0343/ ) says that 'With' can be substituted as follows:

        mgr = (EXPR)
        exit = mgr.__exit__  # Not calling it yet
        value = mgr.__enter__()
        exc = True
        try:
            try:
                VAR = value  # Only if "as VAR" is present
                BLOCK
            except:
                # The exceptional case is handled here
                exc = False
                if not exit(*sys.exc_info()):
                    raise
                # The exception is swallowed if exit() returns true
        finally:
            # The normal and non-local-goto cases are handled here
            if exc:
                exit(None, None, None)

and that "The details of the above translation are intended to prescribe the exact semantics.". This implies that sys.exc_info() would be set when exit is invoked.

I'm finding in practice that sys.exc_info() is not set when __exit__() is invoked in the exceptional case.   I attached a simple repro (repro.py) to demonstrate exactly what I mean.

Can somebody confirm this is the expected behavior?

Thanks,
Mike
http://blogs.msdn.com/jmstall


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