Some time ago Victor proposed in issue16445 a large patch (275 changes) which replaces "Py_DECREF(expr); expr = NULL;" to safer "Py_CLEAR(expr);". That patch contained was so large because it included cases where expr is just a local variable, which are safe in general.

Here are much simpler patches which make replacements only for complex expressions.

These patches (as Victor patch) are generated automatically by the Coccinelle tool (http://coccinelle.lip6.fr/).

Patches are generated by following command:

spatch --in-place --sp-file py_clear.spatch --dir .

LGTM.  If it compiles cleanly and passes the unit test suite--which obviously it should--you may check the 3.4 patch to trunk.

And here is a patch which replaces "Py_XDECREF(identifier); identifier = NULL;" to "Py_CLEAR(identifier);" (10 replaces in 7 files). It doesn't fix any bug (unless identifier is global variable), but makes a code a little cleaner. Compilers should generate equivalent code for both writing. It would be good to commit it too.

Nice work, LGTM!

New changeset 6b10943a5916 by Serhiy Storchaka in branch '2.7':
Issue #20437: Fixed 43 potential bugs when deleting objects references.
http://hg.python.org/cpython/rev/6b10943a5916

New changeset 6adac0d9b933 by Serhiy Storchaka in branch '3.3':
Issue #20437: Fixed 21 potential bugs when deleting objects references.
http://hg.python.org/cpython/rev/6adac0d9b933

New changeset 3110fb3095a2 by Serhiy Storchaka in branch 'default':
Issue #20437: Fixed 22 potential bugs when deleting objects references.
http://hg.python.org/cpython/rev/3110fb3095a2

Thanks Larry and Antoine for your reviews.