      "* Space: O(1)\n",
      "\n",
      "### Pop\n",
      "\n",
      "* If stack is empty, return NULL\n",
      "* Else \n",
      "    * Save top's value\n",
      "    * Set top to top.next\n",
      "    * Return saved value\n",
      "\n",
 
</s> remove     "* If stack is empty, return NULL\n",
 </s> add     "* If stack is empty, return None\n", </s> remove     "* If data we are finding is NULL, return\n",
 </s> add     "* If data we are finding is None, return\n", </s> remove     "* Else, return NULL\n",
 </s> add     "* Else, return None\n", </s> remove     "* If data we are deleting is NULL, return\n",
 </s> add     "* If data we are deleting is None, return\n", </s> remove     "* If the data we are inserting is NULL, return\n",
 </s> add     "* If the data we are inserting is None, return\n",
    "* If stack is empty, return None\n",
      "* Space: O(1)\n",
      "\n",
      "### Pop\n",
      "\n",
    "* If stack is empty, return None\n",
      "* Else \n",
      "    * Save top's value\n",
      "    * Set top to top.next\n",
      "    * Return saved value\n",
      "\n",
keep keep keep keep replace keep keep keep keep keep
 Changed discussions of NULL to None to be more Pythonic. 
stacks_queues/stack/stack_solution.ipynb