      "            self.last.next = node\n",
      "            self.last = node\n",
      "\n",
      "    def dequeue(self):\n",
      "        # Empty list\n",
      "        if self.first is None and self.last is None:\n",
      "            return None\n",
      "        \n",
      "        # Remove only element from a one element list\n",
      "        elif self.first == self.last:\n",
      "            data = self.first.data\n",
      "            self.first = None\n",
      "            self.last = None\n",
      "            return data\n",
      "        else:\n",
      "            data = self.first.data\n",
      "            self.first = self.first.next\n",
      "            return data"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
 
</s> remove     "        node = Node(data)\n",
    "        if self.first is None and self.last is None:\n",
    "            self.first = node\n",
    "            self.last = node\n",
    "        else:\n",
    "            self.last.next = node\n",
    "            self.last = node\n",
 </s> add     "        # TODO: Implement me\n",
    "        pass\n", </s> remove     "        self.first = None\n",
    "        self.last = None\n",
 </s> add     "        # TODO: Implement me\n",
    "        pass\n", </s> remove     "        self.data = data\n",
    "        self.next = None\n",
 </s> add     "        # TODO: Implement me\n",
    "        pass\n", </s> remove     "    * Set first and last to NULL\n",
 </s> add     "    * Set first and last to None\n", </s> remove     "* If the list is empty, return NULL\n",
 </s> add     "* If the list is empty, return None\n",
    "        # TODO: Implement me\n",
    "        pass"
      "            self.last.next = node\n",
      "            self.last = node\n",
      "\n",
      "    def dequeue(self):\n",
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
    "        # TODO: Implement me\n",
    "        pass"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
keep keep keep keep replace replace replace replace replace replace replace replace replace replace replace replace replace replace keep keep keep keep keep
 Cleared queue challenge code section.  Changed references from NULL to None to be more Pythonic. 
stacks_queues/queue_list/queue_list_challenge.ipynb