[Python-Dev] peps: New PEP 490: Chain exceptions at C level

[Andrew Svetlov]

There is another issue: exception chain is not set up on exception
creation in python code, only on throwing.
Thus I have to assign `__context__` and `__cause__` attributes
manually if I want to call `future.set_exception(exc)` instead of
`raise exc`.

See aiohttp code for usage example:
https://github.com/KeepSafe/aiohttp/blob/931efbd518d0d99522d1cd36b43620657cd07304/aiohttp/client.py#L522

On Thu, Mar 26, 2015 at 11:11 AM, Serhiy Storchaka <storchaka at gmail.com> wrote:
> On 26.03.15 10:08, victor.stinner wrote:
>>
>> https://hg.python.org/peps/rev/7daf3bfd9586
>> changeset:   5741:7daf3bfd9586
>> user:        Victor Stinner <victor.stinner at gmail.com>
>> date:        Thu Mar 26 09:08:08 2015 +0100
>> summary:
>>    New PEP 490: Chain exceptions at C level
>
>
>> +Python 3.5 introduces a new private ``_PyErr_ChainExceptions()`` function
>> which
>> +is enough to chain manually exceptions.
>
>
> It also was added in Python 3.4.3.
>
> I meditar about adding _PyErr_ReplaceException() in 2.7 for simpler
> backporting patches from 3.x.
>
>> +Functions like ``PyErr_SetString()`` don't chain automatically
>> exceptions. To
>> +make usage of ``_PyErr_ChainExceptions()`` easier, new functions are
>> added:
>> +
>> +* PyErr_SetStringChain(exc_type, message)
>> +* PyErr_FormatChaine(exc_type, format, ...)
>
>
> Typo.
>
>> +* PyErr_SetNoneChain(exc_type)
>> +* PyErr_SetObjectChain(exc_type, exc_value)
>
>
> I would first make these functions private, as _PyErr_ChainExceptions().
> After proofing their usefulness in the stdlib, they can be made public.
>
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-- 
Thanks,
Andrew Svetlov