Turning SAWarnings into exceptions

[Chris Withers]

Hi All,

How can I turn SAWarnings into exceptions?

I'm struggling with what to put into the PYTHONWARNINGS environment
variable :-S

cheers,

Chris

[Mike Bayer]

import warnings

warnings.simplefilter("error")

[Chris Withers]

Right, but then a bunch of other errors (ImportWarning?!,
DeprecationWarning, etc) stop execution even reaching the code which
might be causing the SAWarning.

It's really quite disappointing that Python's warning mechanisms don't
report a full traceback...

[Simon King]

According to https://docs.python.org/2/using/cmdline.html#cmdoption-W,
the full form of -W (and PYTHONWARNINGS) is:

action:message:category:module:line

Empty fields are ignored, and unused trailing fields can be left out,
so maybe "error::SAWarning" would work?

Simon

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[Simon King]

OK, so it ought to be:

error::sqlalchemy.exc.SAWarning

...instead, but that doesn't work because of
https://bugs.python.org/issue22543, so you need to do it in code. I
have this in my top-level py.test conftest.py:

@pytest.fixture(scope='session', autouse=True)
def sqlalchemywarnings():
"Convert SQLAlchemy warnings to exceptions"
import sqlalchemy.exc
warnings.simplefilter(
'error',
sqlalchemy.exc.SAWarning
)


Simon

[Michal Petrucha]

On Thu, Sep 15, 2016 at 03:09:44PM +0100, Simon King wrote:
> According to https://docs.python.org/2/using/cmdline.html#cmdoption-W,
> the full form of -W (and PYTHONWARNINGS) is:
>
> action:message:category:module:line
>
> Empty fields are ignored, and unused trailing fields can be left out,
> so maybe "error::SAWarning" would work?

The problem with this is that -W and PYTHONWARNINGS are evaluated
*before* any user code gets imported, which means there is no
SAWarning at that time, so this doesn't work. At least it didn't work
for me when I was trying to do this myself a few months ago, and I
found this as an explanation. (I didn't save a reference, though,
unfortunately.)

What I ended up doing was to enable all warnings, and then whitelist
some of them one by one (IIRC, I only had to restore the default
behavior for ImportError and DeprecationWarning, but I'm not entirely
certain anymore – I'm pretty sure it wasn't more than a small handful,
though, of course, this will also depend on the packages you use).

Good luck,

Michal