diff --git a/README.md b/README.md
index 0995fe8..99b97ec 100755
--- a/README.md
+++ b/README.md
@@ -42,6 +42,8 @@
 
 - Awesome things that you can do in IPython Notebooks (in progress) [[IPython nb](http://nbviewer.ipython.org/github/rasbt/python_reference/blob/master/tutorials/awesome_things_ipynb.ipynb)]
 
+- A collection of useful regular expressions [[IPython nb](http://nbviewer.ipython.org/github/rasbt/python_reference/blob/master/tutorials/useful_regex.ipynb)]
+
 <br>
 
 
@@ -92,7 +94,7 @@ GitHub repository [One-Python-benchmark-per-day](https://github.com/rasbt/One-Py
 
 - Numeric matrix manipulation - The cheat sheet for MATLAB, Python NumPy, R, and Julia [[Markdown](./tutorials/matrix_cheatsheet.md)]
 
-- [Python Book Reviews](./other/python_book_reviews.md)
+- Python Book Reviews [[Markdown](./other/python_book_reviews.md)]
 
 <br>
 
diff --git a/tutorials/useful_regex.ipynb b/tutorials/useful_regex.ipynb
new file mode 100644
index 0000000..1f4c880
--- /dev/null
+++ b/tutorials/useful_regex.ipynb
@@ -0,0 +1,826 @@
+{
+ "metadata": {
+  "name": "",
+  "signature": "sha256:9fd7d5201ce5b97fadad65f2c30cfec993fc83907e04418b032bd1bbdac05ff4"
+ },
+ "nbformat": 3,
+ "nbformat_minor": 0,
+ "worksheets": [
+  {
+   "cells": [
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[Sebastian Raschka](http://sebastianraschka.com)  \n",
+      "\n",
+      "- [Link to this IPython notebook on Github](https://github.com/rasbt/python_reference/blob/master/tutorials/useful_regex.ipynb)  "
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "%load_ext watermark"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 1
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "%watermark -d -v -u -t -z"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "Last updated: 06/07/2014 10:07:02 EDT\n",
+        "\n",
+        "CPython 3.4.1\n",
+        "IPython 2.1.0\n"
+       ]
+      }
+     ],
+     "prompt_number": 2
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<font size=\"1.5em\">[More information](http://nbviewer.ipython.org/github/rasbt/python_reference/blob/master/ipython_magic/watermark.ipynb) about the `watermark` magic command extension.</font>"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<hr>\n",
+      "I would be happy to hear your comments and suggestions.  \n",
+      "Please feel free to drop me a note via\n",
+      "[twitter](https://twitter.com/rasbt), [email](mailto:bluewoodtree@gmail.com), or [google+](https://plus.google.com/+SebastianRaschka).\n",
+      "<hr>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 1,
+     "metadata": {},
+     "source": [
+      "A collection of useful regular expressions"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Sections"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "- [About the `re` module](#About-the-re-module)\n",
+      "- [Identify files via file extensions](#Identify-files-via-file-extensions)\n",
+      "- [Username validation](#Username-validation)\n",
+      "- [Checking for valid email addresses](#Checking-for-valid-email-addresses)\n",
+      "- [Check for a valid URL](#Check-for-a-valid-URL)\n",
+      "- [Checking for integers](#Checking-for-integers)\n",
+      "- [Validating dates](#Validating-dates)\n",
+      "- [Time](#Time)"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "About the `re` module"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "The purpose of this IPython notebook is not to rewrite a detailed tutorial about regular expressions or the in-built Python `re` module, but to collect some useful regular expressions for copy&paste purposes."
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "The complete documentation of the Python `re` module can be found here [https://docs.python.org/3.4/howto/regex.html](https://docs.python.org/3.4/howto/regex.html). Below, I just want to list the most important methods for convenience:"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "- `re.match()`  : Determine if the RE matches at the beginning of the string.\n",
+      "- `re.search()` : Scan through a string, looking for any location where this RE matches.\n",
+      "- `re.findall()` : Find all substrings where the RE matches, and returns them as a list.\n",
+      "- `re.finditer()` : Find all substrings where the RE matches, and returns them as an iterator."
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "If you are using the same regular expression multiple times, it is recommended to compile it for improved performance.\n",
+      "\n",
+      "    compiled_re = re.compile(r'some_regexpr')    \n",
+      "    for word in text:\n",
+      "        match = comp.search(compiled_re))\n",
+      "        # do something with the match\n",
+      "    \n",
+      "**E.g., if we want to check if a string ends with a substring:**"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "import re\n",
+      "\n",
+      "needle = 'needlers'\n",
+      "\n",
+      "# Python approach\n",
+      "print(bool(any([needle.endswith(e) for e in ('ly', 'ed', 'ing', 'ers')])))\n",
+      "\n",
+      "# On-the-fly Regular expression in Python\n",
+      "print(bool(re.search(r'(?:ly|ed|ing|ers)$', needle)))\n",
+      "\n",
+      "# Compiled Regular expression in Python\n",
+      "comp = re.compile(r'(?:ly|ed|ing|ers)$') \n",
+      "print(bool(comp.search(needle)))"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "True\n",
+        "True\n",
+        "True\n"
+       ]
+      }
+     ],
+     "prompt_number": 3
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "%timeit -n 10000 -r 50 bool(any([needle.endswith(e) for e in ('ly', 'ed', 'ing', 'ers')]))\n",
+      "%timeit -n 10000 -r 50 bool(re.search(r'(?:ly|ed|ing|ers)$', needle))\n",
+      "%timeit -n 10000 -r 50 bool(comp.search(needle))"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "10000 loops, best of 50: 2.74 \u00b5s per loop\n",
+        "10000 loops, best of 50: 2.93 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n",
+        "10000 loops, best of 50: 1.28 \u00b5s per loop"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n"
+       ]
+      }
+     ],
+     "prompt_number": 4
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Identify files via file extensions"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "A regular expression to check for file extensions."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = r'(?i)(\\w+)\\.(jpeg|jpg|png|gif|tif|svg)$'\n",
+      "\n",
+      "# remove `(?i)` to make regexpr case-sensitive\n",
+      "\n",
+      "str_true = ('test.gif', \n",
+      "            'image.jpeg', \n",
+      "            'image.jpg',\n",
+      "            'image.TIF'\n",
+      "            )\n",
+      "\n",
+      "str_false = ('test.pdf',\n",
+      "             'test.gif.pdf',\n",
+      "             )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 5
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Username validation"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Checking for a valid user name that has a certain minimum and maximum length.\n",
+      "\n",
+      "Allowed characters:\n",
+      "- letters (upper- and lower-case)\n",
+      "- numbers\n",
+      "- dashes\n",
+      "- underscores"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "min_len = 5 # minimum length for a valid username\n",
+      "max_len = 15 # maximum length for a valid username\n",
+      "\n",
+      "pattern = r\"^(?i)[a-z0-9_-]{%s,%s}$\" %(min_len, max_len)\n",
+      "\n",
+      "# remove `(?i)` to only allow lower-case letters\n",
+      "\n",
+      "\n",
+      "\n",
+      "str_true = ('user123', '123_user', 'Username')\n",
+      "            \n",
+      "str_false = ('user', 'username1234_is-way-too-long', 'user$34354')\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 6
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Checking for valid email addresses"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "A regular expression that captures most email addresses."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = r\"(^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\\.[a-zA-Z0-9-.]+$)\"\n",
+      "\n",
+      "str_true = ('test@mail.com',)\n",
+      "            \n",
+      "str_false = ('testmail.com', '@testmail.com', 'test@mailcom')\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 7
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<font size=\"1px\">source: [http://stackoverflow.com/questions/201323/using-a-regular-expression-to-validate-an-email-address](http://stackoverflow.com/questions/201323/using-a-regular-expression-to-validate-an-email-address)</font>"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Check for a valid URL"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Checks for an URL if a string ...\n",
+      "\n",
+      "- starts with `https://`, or `http://`, or `www.`\n",
+      "- or ends with a dot extension"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^(https?:\\/\\/)?([\\da-z\\.-]+)\\.([a-z\\.]{2,6})([\\/\\w \\.-]*)*\\/?$'\n",
+      "\n",
+      "str_true = ('https://github.com', \n",
+      "            'http://github.com',\n",
+      "            'www.github.com',\n",
+      "            'github.com',\n",
+      "            'test.de',\n",
+      "            'https://github.com/rasbt',\n",
+      "            'test.jpeg' # !!! \n",
+      "            )\n",
+      "            \n",
+      "str_false = ('testmailcom', 'http:testmailcom', )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 8
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<font size=\"1px\">source: [http://code.tutsplus.com/tutorials/8-regular-expressions-you-should-know--net-6149](http://code.tutsplus.com/tutorials/8-regular-expressions-you-should-know--net-6149)</font>"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Checking for integers"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "Positive integers"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^\\d+$'\n",
+      "\n",
+      "str_true = ('123', '1', )\n",
+      "            \n",
+      "str_false = ('abc', '1.1', )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 9
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "Negative integers"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^-\\d+$'\n",
+      "\n",
+      "str_true = ('-123', '-1', )\n",
+      "            \n",
+      "str_false = ('123', '-abc', '-1.1', )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 10
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "All integers"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^-{0,1}\\d+$'\n",
+      "\n",
+      "str_true = ('-123', '-1', '1', '123',)\n",
+      "            \n",
+      "str_false = ('123.0', '-abc', '-1.1', )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 11
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "Positive numbers"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^\\d*\\.{0,1}\\d+$'\n",
+      "\n",
+      "str_true = ('1', '123', '1.234', )\n",
+      "            \n",
+      "str_false = ('-abc', '-123', '-123.0')\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 12
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "Negative numbers"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^-\\d*\\.{0,1}\\d+$'\n",
+      "\n",
+      "str_true = ('-1', '-123', '-123.0', )\n",
+      "            \n",
+      "str_false = ('-abc', '1', '123', '1.234', )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 13
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "All numbers"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^-{0,1}\\d*\\.{0,1}\\d+$'\n",
+      "\n",
+      "str_true = ('1', '123', '1.234', '-123', '-123.0')\n",
+      "            \n",
+      "str_false = ('-abc')\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 14
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<font size=\"1px\">source: [http://stackoverflow.com/questions/1449817/what-are-some-of-the-most-useful-regular-expressions-for-programmers](http://stackoverflow.com/questions/1449817/what-are-some-of-the-most-useful-regular-expressions-for-programmers)</font>"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Validating dates"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Validates dates in `mm/dd/yyyy` format."
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = '^(0[1-9]|1[0-2])\\/(0[1-9]|1\\d|2\\d|3[01])\\/(19|20)\\d{2}$'\n",
+      "\n",
+      "str_true = ('01/08/2014', '12/30/2014', )\n",
+      "            \n",
+      "str_false = ('22/08/2014', '-123', '1/8/2014', '1/08/2014', '01/8/2014')\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 15
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 2,
+     "metadata": {},
+     "source": [
+      "Time"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "[[back to top](#Sections)]"
+     ]
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "12-Hour format"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = r'^(1[012]|[1-9]):[0-5][0-9](\\s)?(?i)(am|pm)$'\n",
+      "\n",
+      "str_true = ('2:00pm', '7:30 AM', '12:05 am', )\n",
+      "            \n",
+      "str_false = ('22:00pm', '14:00', '3:12', '03:12pm', )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 29
+    },
+    {
+     "cell_type": "heading",
+     "level": 3,
+     "metadata": {},
+     "source": [
+      "24-Hour format"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "pattern = r'^([0-1]{1}[0-9]{1}|20|21|22|23):[0-5]{1}[0-9]{1}$'\n",
+      "\n",
+      "str_true = ('14:00', '00:30', )\n",
+      "            \n",
+      "str_false = ('22:00pm', '4:00', )\n",
+      "\n",
+      "for t in str_true:\n",
+      "    assert(bool(re.match(pattern, t)) == True), '%s is not True' %t\n",
+      "\n",
+      "for f in str_false:\n",
+      "    assert(bool(re.match(pattern, f)) == False), '%s is not False' %f"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [],
+     "prompt_number": 33
+    }
+   ],
+   "metadata": {}
+  }
+ ]
+}
\ No newline at end of file