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.
diff --git a/Modules/regexmodule.c b/Modules/regexmodule.c
index d449604..4c7035e 100644
--- a/Modules/regexmodule.c
+++ b/Modules/regexmodule.c
@@ -516,11 +516,8 @@
return NULL;
}
/* _PyString_Resize() decrements npattern on failure */
- if (_PyString_Resize(&npattern, n - v) == 0)
- return npattern;
- else {
- return NULL;
- }
+ _PyString_Resize(&npattern, n - v);
+ return npattern;
}