Channel C++ warnings to Python's warning system

[ischoegl]

At the moment, the C++ code base issues warning messages via warn_deprecated and warn_user (the latter introduced in Cantera/cantera#741). In this context, @bryanwweber commented on a new deprecation warning proposed in Cantera/cantera#1084:

One other comment, and I suppose this applies to all the warn_deprecated() calls in C++, I wonder if it's possible to catch those in Python and turn them into real Python DeprecationWarnings so they can be controlled by Python's warning interfaces?

(see here; the same presumably applies to warn_user).

@speth's response was:

I think this would require something a bit like how we interface with Python for writing messages to stdout, that is, registering a handler in the Application class and in that handler making whatever the correct calls are to the Python C API.

Additional context:

• Handle deprecation warnings from all sources consistently in Python cantera#796
• Comment about Boost logger in Improve warning messages in C++  cantera#741

Other thoughts:

As there may be a relatively straight-forward route to this after all, it may make sense to convert this discussion to an enhancement request (i.e. issue).

[speth]

I think this resolved by Cantera/cantera#1201, correct?

[ischoegl]

Feel free!

[speth]

Ah, no such luck -- I think this would just create yet another Issue. I'm going to try another option, which is to assign a different category.

[ischoegl]

just marked it as completed on this end.

[speth]

Yes. To clarify, that's a category I just created for this purpose.

[ischoegl]

👍 Great!

[speth]

Apparently discussions gained a "Close" feature at some point, so now we don't have to rely on categories as an indicator.