      "def merge_sort(data):\n",
      "    if data is None or len(data) < 2:\n",
      "        return data\n",
      "    mid = len(data) // 2\n",
      "    left = data[0:mid]\n",
      "    right = data[mid:]\n",
      "    left = merge_sort(left)\n",
      "    right = merge_sort(right)\n",
      "    return merge(left, right)"
     ]
 
</s> remove    "version": "3.4.3"
 </s> add    "version": "3.5.0" </s> remove    "version": "3.4.3"
 </s> add    "version": "3.5.0"
    "    left = data[:mid]\n",
      "def merge_sort(data):\n",
      "    if data is None or len(data) < 2:\n",
      "        return data\n",
      "    mid = len(data) // 2\n",
    "    left = data[:mid]\n",
      "    right = data[mid:]\n",
      "    left = merge_sort(left)\n",
      "    right = merge_sort(right)\n",
      "    return merge(left, right)"
     ]
keep keep keep keep replace keep keep keep keep keep
 Polish merge sort challenge and solution

Update constraints and code. 
sorting_searching/merge_sort/merge_sort_solution.ipynb