[issue1692335] Fix exception pickling: Move initial args assignment to BaseException.__new__

[Richard Oudkerk]

Richard Oudkerk <shibturn at gmail.com> added the comment:

I realize now that the idea of using object.__reduce__(..., 2) would not really work since many exception classes use non-slot descriptors (unless '__slots__' attributes were also added as hints of what to serialize).

I think there are two options simple enough to sneak in to 3.3:

(1) The trivial patch of initially setting self->args in __new__().

(2) Georg's idea of additionally setting a __newargs__ attribute in __new__() and using it in __reduce__().  However, I would store __newargs__ directly in the struct to avoid always triggering creation of a dict for the instance.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue1692335>
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