[Python-Dev] Big trouble in CVS Python
14 Apr 2003 13:09:04 -0700
On Sun, 2003-04-13 at 13:28, Tim Peters wrote:
> It appears to be a refcount error in recently-added C code that tries to
> generalize the builtin range() function, specifically here:
> Py_XDECREF(istep); <- here
> Word to the wise: don't ever try to reuse a variable whose address is
> passed to PyArg_ParseTuple for anything other than holding what
> PyArg_ParseTuple does or doesn't store into it.
Hmm, then this is my fault. I did exactly that. My approach was to
Py_INCREF an optional argument it if it was given (ie. not NULL),
otherwise to create it from scratch, and Py_DECREF when I was done. I
believe this was a not uncommon idiom (I can't recal the specifics, but
being my first submitted patch, I made sure to try to look for existing
idioms for argument and error handling). I apologize if I erred.
I assume a better approach, then is to get the optional istep
argument, and copy it into a variable for your own use (or create it if
it didn't exist)? ie. Never increment or decrement the optional
argument object, returned from PyArg_ParseTuple, at all?
> You'll never get the
> decrefs straight (and even if you manage to at first, the next person to
> modify your code will break it).
Bingo! Guido took a slightly different approach (and ultimately a
better one, I think), in adapting my patch. Perhaps I unknowingly left
a time bomb for him.
I'll submit a patch to fix this all up tonight, if it hasn't already
been addressed by then.
> only-consumed-eight-hours-this-time<wink>-ly y'rs - tim
Oh, ow! Now that pains me. I am very sorry to hear this wasted so much