[Python-Dev] Py_BuildValue and decref

[Mihai Ibanescu]

On Sun, Sep 10, 2006 at 07:35:59PM +1200, Greg Ewing wrote:
> Barry Warsaw wrote:
> > I just want to point out that the C API documentation is pretty  
> > silent about the refcounting side-effects in error conditions (and  
> > often in success conditions too) of most Python functions.  For  
> > example, what is the refcounting side-effects of PyDict_SetItem() on  
> > val?  What about if that function fails?  Has val been incref'd or  
> > not?  What about the side-effects on any value the new one replaces,  
> > both in success and failure?
> 
> The usual principle is that the refcounting behaviour
> is (or should be) independent of whether the function
> succeeded or failed. In the absence of any statement
> to the contrary in the docs, you should be able to
> assume that.
> 
> The words used to describe the refcount behaviour of
> some functions can be rather confusing, but it always
> boils down to one of two cases: either the function
> "borrows" a reference (and does its own incref if
> needed, the caller doesn't need to care) or it "steals"
> a reference (so the caller is always responsible for
> doing an incref if needed before calling).
> 
> What that rather convoluted comment about PyTuple_SetItem
> is trying to say is just that it *always* steals a reference,
> regardless of whether it succeeds or fails. I expect the
> same is true of Py_BuildValue.

Given that it doesn't seem to be the case, and my quick look at the code
indicates that even internally python is inconsistent, should I file a
low-severity bug so we don't lose track of this?

Misa