docstr: expands size of the array.
  Time Complexity: O(n)
docstr_tok: ["expands","size","of","the","array",".","Time","Complexity",":","O","(","n",")"]
code: def _expand(self):
      """
      expands size of the array.
      Time Complexity: O(n)
      """
      self._array += [None] * len(self._array)
  
imports: from abc import ABCMeta, abstractmethod
label_desc: Use image node_id 6 for calling the ArrayStack obj's underlying member method code with example usage: obj._expand() without return types