diff --git a/benchmarks/timeit_tests.ipynb b/benchmarks/timeit_tests.ipynb
index a183039..4f4ac54 100644
--- a/benchmarks/timeit_tests.ipynb
+++ b/benchmarks/timeit_tests.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:57df5708c2fce146df742136edf2eebb38c32146ab9e612bfd303a086b5bf7d9"
+  "signature": "sha256:5f459d4c7e1521c71838da53736d2fbffd43b39d57d8b653cde1ec9333346574"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -18,6 +18,17 @@
       "[Link to this IPython Notebook on GitHub](https://github.com/rasbt/python_reference/blob/master/benchmarks/timeit_tests.ipynb)"
      ]
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<hr>\n",
+      "I am really looking forward to your comments and suggestions to improve and extend this collection! Just send me a quick note   \n",
+      "via Twitter: [@rasbt](https://twitter.com/rasbt)  \n",
+      "or Email: [bluewoodtree@gmail.com](mailto:bluewoodtree@gmail.com)\n",
+      "<hr>"
+     ]
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
@@ -37,6 +48,8 @@
       "    - [String reversing: [::-1] vs. `''.join(reversed())`](#str_reverse)\n",
       "    - [String concatenation: `+=` vs. `''.join()`](#string_concat)\n",
       "    - [Assembling strings](#string_assembly)  \n",
+      "    - [Testing if a string is an integer](#is_integer)\n",
+      "    - [Testing if a string is a number](#is_number)\n",
       "- [List operations](#list_operations)\n",
       "    - [List reversing: [::-1] vs. reverse() vs. reversed()](#list_reverse)\n",
       "    - [Creating lists using conditional statements](#create_cond_list)\n",
@@ -229,6 +242,8 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
+      "<br>\n",
+      "<br>\n",
       "<a name='string_assembly'></a>\n",
       "## Assembling strings\n",
       "\n",
@@ -294,6 +309,161 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='is_integer'></a>\n",
+      "## Testing if a string is an integer"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "import timeit\n",
+      "\n",
+      "def string_is_int(a_str):\n",
+      "    try:\n",
+      "        int(a_str)\n",
+      "        return True\n",
+      "    except ValueError:\n",
+      "        return False\n",
+      "\n",
+      "an_int = '123'\n",
+      "no_int = '123abc'\n",
+      "\n",
+      "%timeit string_is_int(an_int)\n",
+      "%timeit string_is_int(no_int)\n",
+      "%timeit an_int.isdigit()\n",
+      "%timeit no_int.isdigit()\n",
+      "\n",
+      "#\n",
+      "# Python 3.4.0\n",
+      "# MacOS X 10.9.2\n",
+      "# 2.5 GHz Intel Core i5\n",
+      "# 4 GB 1600 Mhz DDR3\n",
+      "#"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "1000000 loops, best of 3: 401 ns per loop\n",
+        "100000 loops, best of 3: 3.04 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000000 loops, best of 3: 92.1 ns per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000000 loops, best of 3: 96.3 ns per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n"
+       ]
+      }
+     ],
+     "prompt_number": 5
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='is_number'></a>\n",
+      "## Testing if a string is a number"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "import timeit\n",
+      "\n",
+      "def string_is_number(a_str):\n",
+      "    try:\n",
+      "        float(a_str)\n",
+      "        return True\n",
+      "    except ValueError:\n",
+      "        return False\n",
+      "    \n",
+      "a_float = '1.234'\n",
+      "no_float = '123abc'\n",
+      "\n",
+      "a_float.replace('.','',1).isdigit()\n",
+      "no_float.replace('.','',1).isdigit()\n",
+      "\n",
+      "%timeit string_is_number(an_int)\n",
+      "%timeit string_is_number(no_int)\n",
+      "%timeit a_float.replace('.','',1).isdigit()\n",
+      "%timeit no_float.replace('.','',1).isdigit()\n",
+      "\n",
+      "#\n",
+      "# Python 3.4.0\n",
+      "# MacOS X 10.9.2\n",
+      "# 2.5 GHz Intel Core i5\n",
+      "# 4 GB 1600 Mhz DDR3\n",
+      "#"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "1000000 loops, best of 3: 400 ns per loop\n",
+        "1000000 loops, best of 3: 1.15 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000000 loops, best of 3: 452 ns per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "1000000 loops, best of 3: 394 ns per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n"
+       ]
+      }
+     ],
+     "prompt_number": 6
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
       "<a name='list_operations'></a>\n",
       "# List operations"
      ]
@@ -620,6 +790,14 @@
       "### Conclusion\n",
       "Interestingly, the `try-except` loop pays off if we have more elements (here: 1000 integers instead of 100) as dictionary keys to check. Also, it doesn't matter much whether the elements exist or do not exist in the dictionary, yet."
      ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": []
     }
    ],
    "metadata": {}