code: def get_child(self, index: int):
      assert self._children is not None
      assert index >= 0 and index < len(self._children)
      return self._children[index]
  
imports: from abc import ABC, abstractmethod
  from collections import deque
  from copy import deepcopy
  from enum import IntEnum, auto, unique
  from typing import Any
label_desc: Use image node_id 2 for calling the AbstractExpression obj's underlying member method code with example usage: obj.get_child(index) and returns: self