[Python-3000] exception info [was: Discussions with no PEPs] (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Tue Mar 13 10:39:03 CET 2007

Guido van Rossum wrote:

The internal mechanism for bubbling an exception up the stack until an except clause catches it could continue to use the (class, instance, traceback) triple,

Hmmm, so most of that complexity will still be there at the C level. I was hoping there might be some simplification there as well. However...

and if raise is passed a class instead of an instance, the instance would be NULL; when forced to instantiate the exception, the traceback collected up to that point is attached to it.

Would this apply to Python code as well? I.e. if you use a raise statement with a class, it doesn't get instantiated immediately? And if you catch it with an except clause which doesn't capture the exception, it's never instantiated? That would be a bonus.

If an instance was passed to raise, the traceback pointer in the instance is updated each time we leave a stack frame.

So it seems we're back to declaring pre-instantiated exceptions to be bad style, which you said you didn't like earlier -- have you changed your mind?

What about thread safety? Do we just document that using pre-instantiated exceptions is not thread-safe?

-- Greg

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