(Sorry about the length of this email) Python 2.7 deprecated the PyCObject API in favor of a new "capsule" API. http://docs.python.org/dev/whatsnew/2.7.html#capsules The deprecations are set to "ignore" by default, so in theory the API still works: every time an extension uses the API, a deprecation warning is emitted, but then "swallowed" by the filters, and the call succeeds. However, if someone overrides the process-wide warnings settings, then the API can fail altogether, raising a PendingDeprecationWarning exception (which in CPython terms means setting a thread-specific error state and returning NULL). There are at least 15 extension modules that use this API in Fedora 14, and most of the C code I've seen that uses this API doesn't expect it to return NULL. This can lead to hard failures in which /usr/bin/python aborts with an assertion failure (or even a segfault). This has caused at least one app to fail (virt-manager, see bug 620216, due to it modifying the warning settings: fixed), so I've been doublechecking the scope of usage of the PyCObject API, and I've filed bugs against components that are possibly affected: https://bugzilla.redhat.com/showdependencytree.cgi?id=620842&hide_resolved=1 This was on a test machine, so there may be some I've missed. Unfortunately, the list of affected modules includes pygtk2 and pygobject, numpy, selinux, and SWIG. To add to the "fun", the pygtk2/pygobject modules expose the API via macros in a public header file, so that to fix this we'd have to both rebuild those modules, and rebuild users of the header file. You can typically trigger a hard failure of the API via: >>> import warnings >>> warnings.filterwarnings('error') and then try to import one of the affected modules. I've tried to give exact reproducers where I have them in each of the bugs. But if nothing touches the warning settings, you'll never see a problem. Possible ways forward: (a) don't fix this; treat enabling the warning in the "Doctor, it hurts when I do this! So don't do that!" category, and add this to the release notes. Patch Python code that enables the warning so that it doesn't. (b) try to fix the ones that are self-contained; send fixes upstream (c) try to fix them all; send fixes upstream (d) hack the python rpm to remove this warning; this would be a significant change from upstream, given that it's already disabled. One issue here is that this API expresses a binary interface between different Python modules, and that we don't yet have a way to express this at the rpm metadata level. I think we should, to make it easier to track these issues in the future. I don't think it's possible to track these automatically, but we could do it manually. Suggested way to express this: Modules that provide a capsule named "full.dotted.path.to.module.CAPSULENAME" as passed to PyCapsule_Import [1] should have this in their specfile Provides: PyCapsule(full.dotted.path.to.module.CAPSULENAME) for the subpackage holding the module in its %files manifest. Modules that import a capsule should have a corresponding: Requires: PyCapsule(full.dotted.path.to.module.CAPSULENAME) in the appropriate subpackage. So, for example, if we apply the patch I've proposed upstream for pygtk, then pygtk2 should have a: Provides: PyCapsule(gtk._gtk._PyGtk_API) and anything using it needs a: Requires: PyCapsule(gtk._gtk._PyGtk_API) This wouldn't solve all the problems: we'd also need the legacy users of the macro to be rebuilt, and upgrading pygtk2 without upgrading them would lead to a runtime failure when the PyCObject_Ptr call fails (we could potentially supply both hooks, though this would fail if ignoring deprecation warnings was disabled). So upon switching from PyCObject to the capsule API and adding the: Provides above, pygtk2 would also need to add a Conflicts on each of the known users of the API, <= the last version (known to use the broken API); these would then need to be rebuilt, and rpm/yum would have enough information to enforce valid combinations. (None of this seems to address the issue of ABI changes between different supposedly-compatible versions of the API; perhaps we need to treat these capsule names like SONAMEs, and have a numbering within them?) Personally, I'm leaning towards option (a) above (the "don't override warnings" option): closing the various as WONTFIX, and adding a section to the release notes, whilst working towards fixing this in Fedora 15. Affected applications should be patched in Fedora 14 to avoid touching the relevant warning setting, and we'll fix the root cause in Fedora 15. Thoughts? Dave [1] http://docs.python.org/dev/c-api/capsule.html#PyCapsule_Import [2] https://bugzilla.gnome.org/show_bug.cgi?id=623965 -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
