      "            return None\n",
      "        data = self.last_stack.pop()\n",
      "        if not self.last_stack.num_items:\n",
      "            self.stacks.pop()\n",
      "            self.last_stack = self.stacks[-1] \\\n",
      "                if len(self.stacks) else None\n",
      "        return data"
     ]
    },
    {
     "cell_type": "markdown",
 
</s> remove     "        if not self.last_stack.num_items:\n",
 </s> add     "        if self.last_stack.is_empty():\n",
    "            self.last_stack = self.stacks[-1] if self.stacks else None\n",
      "            return None\n",
      "        data = self.last_stack.pop()\n",
      "        if not self.last_stack.num_items:\n",
      "            self.stacks.pop()\n",
    "            self.last_stack = self.stacks[-1] if self.stacks else None\n",
    "            self.last_stack = self.stacks[-1] if self.stacks else None\n",
      "        return data"
     ]
    },
    {
     "cell_type": "markdown",
keep keep keep keep replace replace keep keep keep keep keep
 Update set of stacks challenge solution (#110)

Add is_empty() method, remove extra linebreak. 
stacks_queues/set_of_stacks/set_of_stacks_solution.ipynb