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/cPickle.c b/Modules/cPickle.c
index 2ffba48..a6c5e9d 100644
--- a/Modules/cPickle.c
+++ b/Modules/cPickle.c
@@ -1252,14 +1252,8 @@
*p++ = (char) ch;
}
*p = '\0';
- if (_PyString_Resize(&repr, p - q))
- goto onError;
-
+ _PyString_Resize(&repr, p - q);
return repr;
-
- onError:
- Py_DECREF(repr);
- return NULL;
}