Added CV example link

lec_10_cross_val.ipynb

@@ -15,6 +15,13 @@
       "Cross Validation: The Right and Wrong Way"
      ]
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "*For a real-world example that showcases the pitfalls of improper cross validation, see [this blog post.](http://followthedata.wordpress.com/2013/10/30/the-importance-of-proper-cross-validation-and-experimental-design/)*"
+     ]
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
@@ -84,7 +91,7 @@
       "x = make_x(20)\n",
       "y = hidden_model(x)\n",
       "\n",
-      "print x.shape"
+      "print(x.shape)"
      ],
      "language": "python",
      "metadata": {},
@@ -112,7 +119,7 @@
      "input": [
       "selector = SelectKBest(f_regression, k=2).fit(x, y)\n",
       "best_features = np.where(selector.get_support())[0]\n",
-      "print best_features"
+      "print(best_features)"
      ],
      "language": "python",
      "metadata": {},
@@ -180,7 +187,7 @@
      "input": [
       "xt = x[:, best_features]\n",
       "clf = LinearRegression().fit(xt, y)\n",
-      "print \"Score is \", clf.score(xt, y)"
+      "print(\"Score is \", clf.score(xt, y))"
      ],
      "language": "python",
      "metadata": {},
@@ -385,7 +392,7 @@
       "plt.xlabel(\"Predicted\")\n",
       "plt.ylabel(\"Observed\")\n",
       "\n",
-      "print \"CV Score is \", np.mean(scores)"
+      "print(\"CV Score is \", np.mean(scores))"
      ],
      "language": "python",
      "metadata": {},