[Python-Dev] Warning Framework (PEP 230)

[Guido van Rossum]

> 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!

My first version imported warnings at the start of the program, but
this almost doubled the start-up time, hence the design where the
module is imported only when needed.

The most convenient place to create the Warning category classes is in
the _exceptions module; doing it the easiest way there means that they
are automatically exported to __builtin__.  This doesn't bother me
enough to try and hide them.

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