[issue23188] Provide a C helper function to chain raised (but not yet caught) exceptions

[Eric Snow]

Eric Snow <ericsnowcurrently at gmail.com> added the comment:

FTR, see PEP 490 ("Chain exceptions at C level") which proposed implicitly chaining exceptions in the PyErr_* API.

While that PEP was rejected (not all exceptions should be chained), it does make a good point about the clunkiness of using _PyErr_ChainExceptions():

    PyObject *exc, *val, *tb;
    PyErr_Fetch(&exc, &val, &tb);
    PyErr_Format(ZipImportError, "can't open Zip file: %R", archive);
    _PyErr_ChainExceptions(exc, val, tb);

So if we are going to add a public helper function, let's consider adding one that simplifies usage.  For instance, how about one that indicates the next exception set should chain:

    PyErr_ChainNext();
    PyErr_Format(ZipImportError, "can't open Zip file: %R", archive);

Or perhaps we should revive PEP 490 with an opt out mechanism for the cases where we don't want chaining:

    PyErr_NoChainNext();
    PyErr_Format(PyExc_RuntimeError, "uh-oh");

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nosy: +eric.snow, vstinner
versions: +Python 3.8 -Python 3.7

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<https://bugs.python.org/issue23188>
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