embedding problem with dictionary

[Howard Lightstone]

Following up on myself after "Finding the Problems" (two of them):


>     pnd=PyDict_GetItemString(idict,basename); // borrowed reference
>     if (!pnd)
>      {
>        // must "create" such a subdictionary
>        pnd=PyDict_New();          // new reference
>        // add reference into main dict
>        PyDict_SetItemString(idict,basename,pnd);
>        // always leave with valid pnd
>      }

The problem here is that the dictionary-within-a-dictionary was sometimes 
None.  I was only checking for NULL output from PyDict_GetItemString.

The new test became
     if (!pnd || pnd == Py_None)

This works because None is a singleton (it actually IS documented, just not 
obvious the first time).  And I forgot about None as a possibility.


The second problem was reference counting.
The code below worked sometimes but not others.


> static PyObject * idict;
>
> static PyObject *
> pyaccess_Run(PyObject *self, PyObject *args)
> {
>
>    if (idict)    	    	    	    	             <==REMOVED
>        Py_DECREF(idict)                            <==REMOVED
>    if (!PyArg_ParseTuple(args, "O",&idict)) 
>        return NULL;

Of course, carefull reading of the docs again and again pointed me to the 
fact that the outputs of PyArg_ParseTuple are BORROWED references.  I 
deleted the spurious DECREF above it and things began working reliably.  I 
assume that when it didn't work, the object had been destroyed somehow when 
I erroneously DECREF'ed it.

Even though I have read the embedding docs many times, it seems I don't 
"see" the key phrases when I need them.  I need a little hammer that smacks 
me on the head at those subtle points.