[Python-Dev] Deprecating C APIs (Use of PyArg_NoArgs()) (original) (raw)

Neal Norwitz neal@metaslash.com
Tue, 02 Apr 2002 09:35:18 -0500

"M.-A. Lemburg" wrote:

I think we should come up with a better way to deprecate C level APIs. NEWS is not as effective as one might wish; any deprecation or removal of an API should also include upgrade information for the C extension writer so that upgrading their modules does not require diving into the new style C API code every time.

I'd suggest to have a PEP which documents all C API changes or deprecations together with a short decsription of how to update old code.

I think a PEP will be ignored just as easily as NEWS.

Perhaps, we could wrap all deprecated functions/macros in:

#ifdef Py_DEPRECATED #endif

So if an extension wants to use deprecated functions, they would need to #define Py_DEPRECATED. We could also use another macro Py_OBSOLETE. In this way functions/macros would move into Py_DEPRECATED, then Py_OBSOLETE, then removed.

The functions would still be in a library. And when a function is used a warning would be produced since there is no prototype. Not sure how to handle macros, should they remain undefined and create errors?

If we wanted to be more heavy handed, we could create errors that would force extensions to be compiled w/Py_DEPRECATED by doing:

#ifdef Py_DEPRECATED #define Py_MACRO(a) do_something(a) int Py_prototype(...); #else /* Create a syntax error unless Py_DEPRECATED is defined */ #define Py_MACRO(a) === #define Py_prototype === #endif

Another aspect which we ought to consider is that C extension writers may have a different view of when to leave backward compatibility path in favour of a new Python version. IMHO, there should always be a way to emulate old behaviour so that extensions can continue to support Python 1.5.2 if they need to.

Perhaps, we could put the deprecated functions into a libpythoncompat.a. It would probably be best to move the functions out of the code they are in and into a new compat.c module.

I'm not sure how workable this idea is.

Neal