Added closure snippet.

core/functions.ipynb

@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:a37a234cd37895919493dabe7ab645bb2b5e24d9b304ab564e18b59eac4f7a0a"
+  "signature": "sha256:1c8db5161bc70c65141de06823a3be29e8f58e1668a4090282d39002eabd8adb"
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  "nbformat": 3,
  "nbformat_minor": 0,
@@ -200,6 +200,95 @@
       }
      ],
      "prompt_number": 7
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "## Closures"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Closures are dynamically-genearated functions returned by another function.  The returned function has access to the variables in the local namespace where it was created."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def make_closure(x):\n",
+      "    def closure():\n",
+      "        print('Secret value is: %s' % x)\n",
+      "    return closure\n",
+      "\n",
+      "closure = make_closure(7)\n",
+      "closure()"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "Secret value is: 7\n"
+       ]
+      }
+     ],
+     "prompt_number": 31
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "The following function returns a function that keeps track of arguments it has seen."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def make_watcher():\n",
+      "    dict_seen = {}\n",
+      "    \n",
+      "    def watcher(x):\n",
+      "        if x in dict_seen:\n",
+      "            return True\n",
+      "        else:\n",
+      "            dict_seen[x] = True\n",
+      "            return False\n",
+      "        \n",
+      "    return watcher"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 34
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "watcher = make_watcher()\n",
+      "seq = [1, 1, 2, 3, 5, 8, 13, 2, 5, 13]\n",
+      "[watcher(x) for x in seq]"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "metadata": {},
+       "output_type": "pyout",
+       "prompt_number": 46,
+       "text": [
+        "[False, True, False, False, False, False, False, True, True, True]"
+       ]
+      }
+     ],
+     "prompt_number": 46
     }
    ],
    "metadata": {}