Function PLy_modify_tuple

src/pl/plpython/plpy_exec.c:925–1055

* Apply changes requested by a MODIFY return from a trigger function. */

 * Apply changes requested by a MODIFY return from a trigger function.
 */
static HeapTuple
PLy_modify_tuple(PLyProcedure *proc, PyObject *pltd, TriggerData *tdata,
				 HeapTuple otup)
{
	HeapTuple	rtup;
	PyObject   *volatile plntup;
	PyObject   *volatile plkeys;
	PyObject   *volatile plval;
	Datum	   *volatile modvalues;
	bool	   *volatile modnulls;
	bool	   *volatile modrepls;
	ErrorContextCallback plerrcontext;

	plerrcontext.callback = plpython_trigger_error_callback;
	plerrcontext.previous = error_context_stack;
	error_context_stack = &plerrcontext;

	plntup = plkeys = plval = NULL;
	modvalues = NULL;
	modnulls = NULL;
	modrepls = NULL;

	PG_TRY();
	{
		TupleDesc	tupdesc;
		int			nkeys,
					i;

		if ((plntup = PyDict_GetItemString(pltd, "new")) == NULL)
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_OBJECT),
					 errmsg("TD[\"new\"] deleted, cannot modify row")));
		Py_INCREF(plntup);
		if (!PyDict_Check(plntup))
			ereport(ERROR,
					(errcode(ERRCODE_DATATYPE_MISMATCH),
					 errmsg("TD[\"new\"] is not a dictionary")));

		plkeys = PyDict_Keys(plntup);
		nkeys = PyList_Size(plkeys);

		tupdesc = RelationGetDescr(tdata->tg_relation);

		modvalues = (Datum *) palloc0(tupdesc->natts * sizeof(Datum));
		modnulls = (bool *) palloc0(tupdesc->natts * sizeof(bool));
		modrepls = (bool *) palloc0(tupdesc->natts * sizeof(bool));

		for (i = 0; i < nkeys; i++)
		{
			PyObject   *platt;
			char	   *plattstr;
			int			attn;
			PLyObToDatum *att;

			platt = PyList_GetItem(plkeys, i);
			if (PyString_Check(platt))
				plattstr = PyString_AsString(platt);
			else if (PyUnicode_Check(platt))