add comments related to use of DECREF

src/array.cc

@@ -1716,7 +1716,6 @@ PyObject *reduce(PyObject *self_, PyObject*)
     self->ndim_shape(&ndim, &shape);
     size_t size_in_bytes = calc_size(ndim, shape) * sizeof(T);
 
-    Py_INCREF(reconstruct);
     PyObject *pyshape = PyTuple_New(ndim);
     for (int i=0; i < ndim; ++i)
         PyTuple_SET_ITEM(pyshape, i, PyInt_FromSize_t(shape[i]));
@@ -1724,9 +1723,11 @@ PyObject *reduce(PyObject *self_, PyObject*)
     PyObject *data = PyBytes_FromStringAndSize((char*)self->data(),
                                                 size_in_bytes);
 
+    // PyTuple_SET_ITEM steals references, so we need to INCREF
+    Py_INCREF(reconstruct);
     PyTuple_SET_ITEM(result, 0, reconstruct);
+    // Py_BuildValue does not steal references, so we need to DECREF
     PyTuple_SET_ITEM(result, 1, Py_BuildValue("(OOO)", pyshape, format, data));
-
     Py_DECREF(pyshape);
     Py_DECREF(format);
     Py_DECREF(data);