       "name": "stdout",
       "output_type": "stream",
       "text": [
        "Test: insert_to_front on an empty list\n",
        "Test: insert_to_front on a NULL\n",
        "Test: insert_to_front general case\n",
        "Success: test_insert_to_front\n",
        "\n",
        "Test: append on an empty list\n",
        "Test: append a NULL\n",
 
</s> remove       "Test: append a NULL\n",
 </s> add       "Test: append a None\n", </s> remove       "Test: find a NULL\n",
 </s> add       "Test: find a None\n", </s> remove       "Test: NULL towers\n",
 </s> add       "Test: None towers\n", </s> remove       "Test: delete a NULL\n",
 </s> add       "Test: delete a None\n", </s> remove         print('Test: insert_to_front on a NULL')
 </s> add         print('Test: insert_to_front on a None')
      "Test: insert_to_front on a None\n",
       "name": "stdout",
       "output_type": "stream",
       "text": [
        "Test: insert_to_front on an empty list\n",
      "Test: insert_to_front on a None\n",
        "Test: insert_to_front general case\n",
        "Success: test_insert_to_front\n",
        "\n",
        "Test: append on an empty list\n",
        "Test: append a NULL\n",
keep keep keep keep replace keep keep keep keep keep
 Changed discussions of NULL to None to be more Pythonic. 
linked_lists/linked_list/linked_list_solution.ipynb