diff --git a/recursion_dynamic/hanoi/hanoi_challenge.ipynb b/recursion_dynamic/hanoi/hanoi_challenge.ipynb
index b03217d..624f168 100644
--- a/recursion_dynamic/hanoi/hanoi_challenge.ipynb
+++ b/recursion_dynamic/hanoi/hanoi_challenge.ipynb
@@ -35,6 +35,10 @@
     "## Constraints\n",
     "\n",
     "* Can we assume we already have a stack class that can be used for this problem?\n",
+    "    * Yes\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * No\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -44,8 +48,8 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* None tower(s)\n",
-    "* 0 disks\n",
+    "* None tower(s) -> Exception\n",
+    "* 0 disks -> None\n",
     "* 1 disk\n",
     "* 2 or more disks"
    ]
@@ -86,9 +90,11 @@
    },
    "outputs": [],
    "source": [
-    "def hanoi(num_disks, src, dest, buff):\n",
-    "    # TODO: Implement me\n",
-    "    pass"
+    "class Hanoi(object):\n",
+    "\n",
+    "    def move_disks(self, num_disks, src, dest, buff):\n",
+    "        # TODO: Implement me\n",
+    "        pass"
    ]
   },
   {
@@ -111,35 +117,36 @@
    "outputs": [],
    "source": [
     "# %load test_hanoi.py\n",
-    "from nose.tools import assert_equal\n",
+    "from nose.tools import assert_equal, assert_raises\n",
     "\n",
     "\n",
     "class TestHanoi(object):\n",
     "\n",
     "    def test_hanoi(self):\n",
+    "        hanoi = Hanoi()\n",
     "        num_disks = 3\n",
     "        src = Stack()\n",
     "        buff = Stack()\n",
     "        dest = Stack()\n",
     "\n",
     "        print('Test: None towers')\n",
-    "        hanoi(num_disks, None, None, None)\n",
+    "        assert_raises(TypeError, hanoi.move_disks, num_disks, None, None, None)\n",
     "\n",
     "        print('Test: 0 disks')\n",
-    "        hanoi(num_disks, src, dest, buff)\n",
+    "        hanoi.move_disks(num_disks, src, dest, buff)\n",
     "        assert_equal(dest.pop(), None)\n",
     "\n",
     "        print('Test: 1 disk')\n",
     "        src.push(5)\n",
-    "        hanoi(num_disks, src, dest, buff)\n",
+    "        hanoi.move_disks(num_disks, src, dest, buff)\n",
     "        assert_equal(dest.pop(), 5)\n",
     "\n",
     "        print('Test: 2 or more disks')\n",
-    "        for i in range(num_disks, -1, -1):\n",
-    "            src.push(i)\n",
-    "        hanoi(num_disks, src, dest, buff)\n",
-    "        for i in range(0, num_disks):\n",
-    "            assert_equal(dest.pop(), i)\n",
+    "        for disk_index in range(num_disks, -1, -1):\n",
+    "            src.push(disk_index)\n",
+    "        hanoi.move_disks(num_disks, src, dest, buff)\n",
+    "        for disk_index in range(0, num_disks):\n",
+    "            assert_equal(dest.pop(), disk_index)\n",
     "\n",
     "        print('Success: test_hanoi')\n",
     "\n",
@@ -165,21 +172,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,
diff --git a/recursion_dynamic/hanoi/hanoi_solution.ipynb b/recursion_dynamic/hanoi/hanoi_solution.ipynb
index b974912..785a8fd 100644
--- a/recursion_dynamic/hanoi/hanoi_solution.ipynb
+++ b/recursion_dynamic/hanoi/hanoi_solution.ipynb
@@ -34,6 +34,10 @@
     "## Constraints\n",
     "\n",
     "* Can we assume we already have a stack class that can be used for this problem?\n",
+    "    * Yes\n",
+    "* Can we assume the inputs are valid?\n",
+    "    * No\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -43,8 +47,8 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* None tower(s)\n",
-    "* 0 disks\n",
+    "* None tower(s) -> Exception\n",
+    "* 0 disks -> None\n",
     "* 1 disk\n",
     "* 2 or more disks"
    ]
@@ -93,14 +97,19 @@
    },
    "outputs": [],
    "source": [
-    "def hanoi(num_disks, src, dest, buff):\n",
-    "    if src is None or dest is None or buff is None:\n",
-    "        return\n",
-    "    if num_disks > 0:\n",
-    "        hanoi(num_disks-1, src, buff, dest)\n",
-    "        data = src.pop()\n",
-    "        dest.push(data)\n",
-    "        hanoi(num_disks-1, buff, dest, src)"
+    "class Hanoi(object):\n",
+    "\n",
+    "    def move_disks(self, num_disks, src, dest, buff):\n",
+    "        if src is None or dest is None or buff is None:\n",
+    "            raise TypeError('Cannot have a None input')\n",
+    "        self._move_disks(num_disks, src, dest, buff)\n",
+    "\n",
+    "    def _move_disks(self, num_disks, src, dest, buff):\n",
+    "        if num_disks == 0:\n",
+    "            return\n",
+    "        self.move_disks(num_disks-1, src, buff, dest)\n",
+    "        dest.push(src.pop())\n",
+    "        self.move_disks(num_disks-1, buff, dest, src)"
    ]
   },
   {
@@ -128,35 +137,36 @@
    ],
    "source": [
     "%%writefile test_hanoi.py\n",
-    "from nose.tools import assert_equal\n",
+    "from nose.tools import assert_equal, assert_raises\n",
     "\n",
     "\n",
     "class TestHanoi(object):\n",
     "\n",
     "    def test_hanoi(self):\n",
+    "        hanoi = Hanoi()\n",
     "        num_disks = 3\n",
     "        src = Stack()\n",
     "        buff = Stack()\n",
     "        dest = Stack()\n",
     "\n",
     "        print('Test: None towers')\n",
-    "        hanoi(num_disks, None, None, None)\n",
+    "        assert_raises(TypeError, hanoi.move_disks, num_disks, None, None, None)\n",
     "\n",
     "        print('Test: 0 disks')\n",
-    "        hanoi(num_disks, src, dest, buff)\n",
+    "        hanoi.move_disks(num_disks, src, dest, buff)\n",
     "        assert_equal(dest.pop(), None)\n",
     "\n",
     "        print('Test: 1 disk')\n",
     "        src.push(5)\n",
-    "        hanoi(num_disks, src, dest, buff)\n",
+    "        hanoi.move_disks(num_disks, src, dest, buff)\n",
     "        assert_equal(dest.pop(), 5)\n",
     "\n",
     "        print('Test: 2 or more disks')\n",
-    "        for i in range(num_disks, -1, -1):\n",
-    "            src.push(i)\n",
-    "        hanoi(num_disks, src, dest, buff)\n",
-    "        for i in range(0, num_disks):\n",
-    "            assert_equal(dest.pop(), i)\n",
+    "        for disk_index in range(num_disks, -1, -1):\n",
+    "            src.push(disk_index)\n",
+    "        hanoi.move_disks(num_disks, src, dest, buff)\n",
+    "        for disk_index in range(0, num_disks):\n",
+    "            assert_equal(dest.pop(), disk_index)\n",
     "\n",
     "        print('Success: test_hanoi')\n",
     "\n",
@@ -196,21 +206,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.5.0"
   }
  },
  "nbformat": 4,
diff --git a/recursion_dynamic/hanoi/test_hanoi.py b/recursion_dynamic/hanoi/test_hanoi.py
index 7fa113d..f100254 100644
--- a/recursion_dynamic/hanoi/test_hanoi.py
+++ b/recursion_dynamic/hanoi/test_hanoi.py
@@ -1,32 +1,33 @@
-from nose.tools import assert_equal
+from nose.tools import assert_equal, assert_raises
 
 
 class TestHanoi(object):
 
     def test_hanoi(self):
+        hanoi = Hanoi()
         num_disks = 3
         src = Stack()
         buff = Stack()
         dest = Stack()
 
         print('Test: None towers')
-        hanoi(num_disks, None, None, None)
+        assert_raises(TypeError, hanoi.move_disks, num_disks, None, None, None)
 
         print('Test: 0 disks')
-        hanoi(num_disks, src, dest, buff)
+        hanoi.move_disks(num_disks, src, dest, buff)
         assert_equal(dest.pop(), None)
 
         print('Test: 1 disk')
         src.push(5)
-        hanoi(num_disks, src, dest, buff)
+        hanoi.move_disks(num_disks, src, dest, buff)
         assert_equal(dest.pop(), 5)
 
         print('Test: 2 or more disks')
-        for i in range(num_disks, -1, -1):
-            src.push(i)
-        hanoi(num_disks, src, dest, buff)
-        for i in range(0, num_disks):
-            assert_equal(dest.pop(), i)
+        for disk_index in range(num_disks, -1, -1):
+            src.push(disk_index)
+        hanoi.move_disks(num_disks, src, dest, buff)
+        for disk_index in range(0, num_disks):
+            assert_equal(dest.pop(), disk_index)
 
         print('Success: test_hanoi')