diff --git a/ProgrammingAssignment_1/model.ipynb b/ProgrammingAssignment_1/model.ipynb
index 36ac14dc31575cbea231c2830566cd54a17ac9c9..dcfb2390ae89af6cf83559eca7671c93fe940147 100644
--- a/ProgrammingAssignment_1/model.ipynb
+++ b/ProgrammingAssignment_1/model.ipynb
@@ -122,7 +122,12 @@
     "    Returns:\n",
     "        dist: float\n",
     "    '''\n",
-
+    "if metric == 'Euclidean':\n",
+        "raise NotImplementedError",
+    "elif metric == 'Manhattan':\n",
+        "raise NotImplementedError\n",
+    "else:\n",
+        "raise ValueError('{} is not a valid metric.'.format(metric))\n",
     "    return dist # scalar distance btw x and y"
    ]
   },