[Python-Dev] Warning Framework (PEP 230)

[Guido van Rossum]

> Some of my thoughts after reading the PEP and Paul/Guido's exchange.
> 
> - A function in the warn module is better than one in the sys module.
>   "from warnings import warn" is good enough to not warrant a
>   built-in.  I get the sense that the PEP description is behind
>   Guido's currently implementation here.

Yes.  I've updated the PEP to match the (2nd) implementation.

> - When PyErr_Warn() returns 1, does that mean a warning has been
>   transmuted into an exception, or some other exception occurred
>   during the setting of the warning?  (I think I know, but the PEP
>   could be clearer here).

I've clarified this now: it returns 1 in either case.  You have to do
exception handling in either case.  I'm not telling why -- you don't
need to know.  The caller of PyErr_Warn() should not attempt to catch
the exception -- if that's your intent, you shouldn't be calling
PyErr_Warn().  And PyErr_Warn() is complicated enough that it has to
allow raising an exception.

> - It would be nice if lineno can be a range specification.  Other
>   matches are based on regexps -- think of this as a line number
>   regexp.

Too much complexity already.

> - Why not do setupwarnings() in site.py?

See the PEP and the current implementation.  The delayed-loading of
the warnings module means that we have to save the -W options as
sys.warnoptions.  (This also makes them work when multiple
interpreters are used -- they all get the -W options.)

> - Regexp matching on messages should be case insensitive.

Good point!  Done in my version of the code.

> - The second argument to sys.warn() or PyErr_Warn() can be any class,
>   right?

Almost.  It must be derived from __builtin__.Warning.

>   If so, it's easy for me to have my own warning classes.
>   What if I want to set up my own warnings filters?  Maybe if `action'
>   could be a callable as well as a string.  Then in my IDE, I could
>   set that to "mygui.popupWarningsDialog".

No, for that purpose you would override warnings.showwarning().

--Guido van Rossum (home page: http://www.python.org/~guido/)