      {
       "name": "stdout",
       "output_type": "stream",
       "text": [
        "Test: NULL towers\n",
        "Test: 0 disks\n",
        "Test: 1 disk\n",
        "Test: 2 or more disks\n",
        "Success: test_hanoi\n"
       ]
 
</s> remove       "Test: insert_to_front on a NULL\n",
 </s> add       "Test: insert_to_front on a None\n", </s> remove     "* NULL tower(s)\n",
 </s> add     "* None tower(s)\n", </s> remove     "* NULL tower(s)\n",
 </s> add     "* None tower(s)\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",
      "Test: None towers\n",
      {
       "name": "stdout",
       "output_type": "stream",
       "text": [
      "Test: None towers\n",
        "Test: 0 disks\n",
        "Test: 1 disk\n",
        "Test: 2 or more disks\n",
        "Success: test_hanoi\n"
       ]
keep keep keep keep replace keep keep keep keep keep
 Changed discussions of NULL to None to be more Pythonic. 
stacks_queues/hanoi/hanoi_solution.ipynb