py3: fix artificial exception test in sphinxbuild.py

[jdemeyer]

This test is raising an exception and then it tries to display the traceback, long after the exception has been handled by the doctest framework. In Python 3 (and also after #24986), exceptions do not stay alive forever. The solution is fixing the test to construct the traceback in an except Exception block.

sage -t src/sage_setup/docbuild/sphinxbuild.py
**********************************************************************
File "src/sage_setup/docbuild/sphinxbuild.py", line 212, in sage_setup.docbuild.sphinxbuild.SageSphinxLogger._log_line
Failed example:
    for line in traceback.format_exc().split('\n'):
        logger._log_line(line)
Expected:
    [#25160   ] Traceback (most recent call last):
    [#25160   ]   File ...
    [#25160   ]     self.compile_and_execute(example, compiler, test.globs)
    [#25160   ]   File ...
    [#25160   ]     exec(compiled, globs)
    [#25160   ]   File ...
    [#25160   ]     raise Exception("artificial exception")
    [#25160   ] Exception: artificial exception
Got:
    [#25160   ] NoneType: None
**********************************************************************

While I was at it, I fixed one more trivial doctest failure. All tests in src/sage_setup/docbuild now pass on Python 3.

[embray]

That makes sense--I agree the test is not good in the first place. Though I don't exactly understand why this changed. Just because of the sys.exc_clear()?

It makes sense though--the Python 2 behavior of keeping exception objects and tracebacks around long past their applicability was not great to begin with.

[jdemeyer]

Replying to embray:

Just because of the sys.exc_clear()?

Indeed. Python 3 effectively does sys.exc_clear() when leaving the try/except block.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​03a5413

Test type(logger) for py3 compatibility

[embray]

Makes sense, thank you.