backport tim_one's patch: [Re-did unicodeobject.c - it's changed a lot since 2.1 :) Pretty confident that it's correct] Repair widespread misuse of _PyString_Resize. Since it's clear people don't understand how this function works, also beefed up the docs. The most common usage error is of this form (often spread out across gotos): if (_PyString_Resize(&s, n) < 0) { Py_DECREF(s); s = NULL; goto outtahere; } The error is that if _PyString_Resize runs out of memory, it automatically decrefs the input string object s (which also deallocates it, since its refcount must be 1 upon entry), and sets s to NULL. So if the "if" branch ever triggers, it's an error to call Py_DECREF(s): s is already NULL! A correct way to write the above is the simpler (and intended) if (_PyString_Resize(&s, n) < 0) goto outtahere; Bugfix candidate. Original patch(es): python/dist/src/Objects/fileobject.c:2.161 python/dist/src/Objects/stringobject.c:2.161 python/dist/src/Objects/unicodeobject.c:2.147