Improve debugging of Expat handlers return value

[picnixz]

Feature or enhancement

Proposal:

While working on #146169, I forgot to add a return value to my ExternalEntityRef handler which caused me to get some weird error like:

    parser.Parse(data, True)
    ~~~~~~~~~~~~^^^^^^^^^^^^
TypeError: 'NoneType' object cannot be interpreted as an integer

The problem is in the RC_HANDLER macro which tries to convert the return value of the handler using some generic constructs. If that conversion, we just reraise, but this is annoying because we don't really know which handler raised. A simple fix is to add an exception note so that we can indicate which handler failed.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-146563: add exception note for invalid Expat handler return values #146565