[Python-Dev] Warning Framework (PEP 230)

[Greg Stein]

On Mon, Dec 11, 2000 at 07:39:31PM -0500, Guido van Rossum wrote:
> > Since you must do "from warnings import warn" before using the warnings,
> > then I think it makes sense to put the Warning classes into the warnings
> > module. (e.g. why increase the size of the builtins?)
> 
> I don't particularly care whether the Warning category classes are
> builtins, but I can't declare them in the warnings module.  Typical
> use from C is:
> 
>     if (PyErr_Warn(PyExc_DeprecationWarning,
> 		   "the strop module is deprecated"))
>             return NULL;
> 
> PyErr_Warn() imports the warnings module on its first call.  But the
> value of PyExc_DeprecationWarning c.s. must be available *before* the
> first call, so they can't be imported from the warnings module!

Do the following:

pywarn.h or pyerrors.h:

#define PyWARN_DEPRECATION "DeprecationWarning"

     ...
     if (PyErr_Warn(PyWARN_DEPRECATION,
 		   "the strop module is deprecated"))
             return NULL;

The PyErr_Warn would then use the string to dynamically look up / bind to
the correct value from the warnings module. By using the symbolic constant,
you will catch typos in the C code (e.g. if people passed raw strings, then
a typo won't be found until runtime; using symbols will catch the problem at
compile time).

The above strategy will allow for fully-delayed loading, and for all the
warnings to be located in the "warnings" module.

Cheers,
-g

-- 
Greg Stein, http://www.lyra.org/