def _move(self, index, new_priority):
item, old_priority = self._memory[index]<EOL>old_priority = old_priority or <NUM_LIT:0><EOL>self._memory[index] = _SumRow(item, new_priority)<EOL>self._update_internal_nodes(index, new_priority - old_priority)<EOL>
Change the priority of a leaf node.