      "    def insert_to_front(self, data):\n",
      "        pass\n",
      "        # TODO: Implement me\n",
      "\n",
      "    def append(self, data, next_node=None):\n",
      "        pass\n",
      "        # TODO: Implement me\n",
      "\n",
      "    def find(self, data):\n",
      "        pass\n",
 
</s> remove     "    def append(self, data, next_node=None):\n",
 </s> add     "    def append(self, data):\n", </s> remove     "            return\n",
    "        node = Node(data)\n",
    "        if self.head is None:\n",
    "            self.head = node\n",
    "        else:\n",
    "            node.next = self.head\n",
    "            self.head = node\n",
 </s> add     "            return None\n",
    "        node = Node(data, self.head)\n",
    "        self.head = node\n", </s> remove     "    def __init__(self, data, next_node=None):\n",
    "        self.next = next_node\n",
 </s> add     "    def __init__(self, data, next=None):\n",
    "        self.next = next\n", </s> remove     "            return\n",
 </s> add     "            return None\n", </s> remove     "            return\n",
    "        node = Node(data, next_node)\n",
 </s> add     "            return None\n",
    "        node = Node(data)\n",
    "    def append(self, data):\n",
      "    def insert_to_front(self, data):\n",
      "        pass\n",
      "        # TODO: Implement me\n",
      "\n",
    "    def append(self, data):\n",
      "        pass\n",
      "        # TODO: Implement me\n",
      "\n",
      "    def find(self, data):\n",
      "        pass\n",
keep keep keep keep replace keep keep keep keep keep
 Polish linked list challenge and solution

Update algorithm discussion, solution, and constraints. 
linked_lists/linked_list/linked_list_challenge.ipynb