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The Problem:
- you embed Python in some app
- the app dynamically loads libexpat of version X
- the embedded Python imports pyexpat (which was built
against
 libexpat version X+n)
--> pyexpat gets the expat symbols from the already
loaded and *older*
 libexpat: crash (Specifically the crash we observed
was in
 getting an old XML_ErrorString (from xmlparse.c)
and then calling
 it with newer values in the XML_Error enum:
 // pyexpat.c, line 1970
 ...
 // Added in Expat 1.95.7.
 MYCONST(XML_ERROR_UNBOUND_PREFIX);
 ...
The Solution:
Prefix all a exported symbols with "PyExpat_". This is
similar to
what Mozilla does for some common libs:
http://lxr.mozilla.org/seamonkey/source/modules/libimg/png/mozpngconf.h#115
I'll attach the gdb backtrace that we were getting and
a patch.

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This seems to be a duplicate of bug #1075984. I like this
patch better, but perhaps both patches (the one here and the
other bug report) should be implemented?
I think Martin helps maintain pyexpat. Maybe he has some
ideas about either or both of these bugs/patches. Martin,
do you think these are safe to apply? I can apply the
patch(es) if you think it's safe.
Trent, is this patch sufficient to meet your embedding needs
so that nothing else needs to be done?
I do not think this patch can be applied to 2.4.

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> This seems to be a duplicate of bug #1075984. 
You are right.
> Trent, is this patch sufficient to meet your embedding
> needs so that nothing else needs to be done?
Yes.
> I do not think this patch can be applied to 2.4.
That's fine. Getting this into Python >=2.5 would be good
enough.
Martin,
Have you had a chance to review this?

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Attempted summary to get this patch into Python 2.5:
As Neal points out this is a duplicate of
<http://python.org/sf/1075984>. The patch on *that* bug
fixes the specific issue, but does not solve the general
problem (as 'mwh' pointed out in the comments there).
I think we should 
1. apply this patch
2. then perhaps update our expat version (see
http://python.org/sf/1433435,
http://mail.python.org/pipermail/python-dev/2006-March/062287.html),
3. then update Modules/expat/pyexpatns.h (that this patch
adds) for any new symbols in the new version of Expat.
Neal, Martin, Michael, what do you think?

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As well, *possibly* the same should be done for Python's
bz2.so, although the only relevant exported symbol is
Util_UnivNewlineRead
 nm bz2.so \
 | grep -v " [a-zBUA] " \
 | grep -v "_fini\|_init\|initbz2"

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Sending Modules/expat/expat_external.h
Adding Modules/expat/pyexpatns.h
Transmitting file data ..
Committed revision 47034.
I upgraded Python's expat to 2.0.0 immediately before and
checked that no new symbols where added (i.e. no new
#define's necessary for the patch).