Make more concrete exercise suggestions for part 4

Author: treyhunner

part-4.ipynb

@@ -417,7 +417,13 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "**Extra Credit:** Try using a list comprehension in the translate function.\n",
+      "**Exercises:**\n",
+      "\n",
+      "1. Make a new py file and put that translate function in the file. Use the print function to print out some examples of using the function.\n",
+      "\n",
+      "2. Refactor the translate function to use a list comprehension.\n",
+      "\n",
+      "3. There are lots of ways to write that translate function.  Just for fun, see if you can write the whole translate function in one line.\n",
       "\n",
       "**Note:** Typing out the exercises for the next section, \"Sets\",  is optional. If your brain is melting, feel free to sit back, relax, and enjoy the rest of the lecture."
      ]