[Python-Dev] Good way of finding out what C functions we have? (original) (raw)

Brett C. bac at OCF.Berkeley.EDU
Tue Sep 30 17:41:12 EDT 2003

Skip Montanaro wrote:

>> I would look in pyconfig.h.in as the first thing. There is a pitfall, >> though: presence of some HAVEfoo in pyconfig.h does not mean that >> Python gracefully deals with the absence of foo. When converting >> configure to autoconf 2.5x, I checked all macros to determine whether >> they were still in use, but some may have become unused/not processed >> correctly since. That would be a bug, of course.

Brett> What does happen if a HAVEfoo is actually required? Does the Brett> build fail or will configure halt and say that the build will Brett> fail if you proceed? It's not exactly clear what you mean by "required".

As in Python will not be at all functional without the functionality being required.

All the HAVEfoo macros are supposed to indicate the presence (when defined) or absence (when not defined) of a particular "feature" which is not felt by one or more of the authors to be universally available. As far as I know, a HAVEfoo macro should never be required to be defined, though I suppose if we had an infinite amount of time on our hands be might code a configure test for HAVEWRITE. HAVE* macros should only be used in a conditional way like

#ifdef HAVEFOO /* assume foo is available */ else /* assume foo is missing and code around its absence */ endif or as in the case of fsync() in posixmodule.c #ifdef HAVEFSYNC /* define wrapper for fsync() endif The lack of a HAVEfoo macro definition might make an entire module unavailable. More often it causes a single module function to not be defined or for a messier or less efficient implementation to be used.

Right. I was wondering if there are any checks in configure.in that if something was not available that Python itself would not compile at all. I would suspect not since that is what the ANSI C/POSIX coding requirement is supposed to handle, right?

-Brett

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