diff --git a/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb b/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
index de36159..3678a4e 100644
--- a/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
+++ b/.ipynb_checkpoints/not_so_obvious_python_stuff-checkpoint.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:a9475a6f1134f87066829ecff7dab70b1fab2b2cc8ae3ee110b3e719b9626c23"
+  "signature": "sha256:2e4322ee7bffc6746194af4b3ac6bb9cd8794c14bea2575e3097821a7d5f9b52"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -63,7 +63,11 @@
       "- [Python's LEGB scope resolution and the keywords `global` and `nonlocal`](#python_legb)\n",
       "- [When mutable contents of immutable tuples aren't so mutable](#immutable_tuple)\n",
       "- [List comprehensions are fast, but generators are faster!?](#list_generator)\n",
-      "- [Public vs. private class methods and name mangling](#private_class)"
+      "- [Public vs. private class methods and name mangling](#private_class)\n",
+      "- [The consequences of modifying a list when looping through it](#looping_pitfall)\n",
+      "- [Dynamic binding and typos in variable names](#dynamic_binding)\n",
+      "- [List slicing using indexes that are \"out of range](#out_of_range_slicing)\n",
+      "- [Reusing global variable names and UnboundLocalErrors](#unboundlocalerror)"
      ]
     },
     {
@@ -515,7 +519,7 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "Don't use mutable objects (e.g., dictionaries, lists, sets, etc.) as default arguments for functions! You might expect that a new list is created every time when we call the function without providing an argument for the default parameter, but this is not the case: Python will create the mutable object (default parameter) the first time the function is defined - not when it is called, see the following code:\n",
+      "Don't use mutable objects (e.g., dictionaries, lists, sets, etc.) as default arguments for functions! You might expect that a new list is created every time when we call the function without providing an argument for the default parameter, but this is not the case: **Python will create the mutable object (default parameter) the first time the function is defined - not when it is called**, see the following code:\n",
       "\n",
       "(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)"
      ]
@@ -548,6 +552,48 @@
      ],
      "prompt_number": 1
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Another good example showing that demonstrates that default arguments are created when the function is created (**and not when it is called!**):"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "import time\n",
+      "def report_arg(my_default=time.time()):\n",
+      "    print(my_default)\n",
+      "\n",
+      "report_arg()\n",
+      "\n",
+      "time.sleep(5)\n",
+      "\n",
+      "report_arg()"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "1397764090.456688\n",
+        "1397764090.456688"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n"
+       ]
+      }
+     ],
+     "prompt_number": 10
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
@@ -1299,6 +1345,358 @@
      ],
      "prompt_number": 28
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='looping_pitfall'></a>\n",
+      "## The consequences of modifying a list when looping through it"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "It can be really dangerous to modify a list when iterating through - it is a very common pitfall that can cause unintended behavior!  \n",
+      "Look at the following examples, and for a fun exercise: try to figure out what is going on before you skip to the solution!"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "a = [1, 2, 3, 4, 5]\n",
+      "for i in a:\n",
+      "    if not i % 2:\n",
+      "        a.remove(i)\n",
+      "print(a)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "[1, 3, 5]\n"
+       ]
+      }
+     ],
+     "prompt_number": 3
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "b = [2, 4, 5, 6]\n",
+      "for i in b:\n",
+      "     if not i % 2:\n",
+      "         b.remove(i)\n",
+      "print(b)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "[4, 5]\n"
+       ]
+      }
+     ],
+     "prompt_number": 4
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "**The solution** is that we are iterating through the list index by index, and if we remove one of the items in-between, we inevitably mess around with the indexing, look at the following example, and it will become clear:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "b = [2, 4, 5, 6]\n",
+      "for index, item in enumerate(b):\n",
+      "    print(index, item)\n",
+      "    if not item % 2:\n",
+      "        b.remove(item)\n",
+      "print(b)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "0 2\n",
+        "1 5\n",
+        "2 6\n",
+        "[4, 5]\n"
+       ]
+      }
+     ],
+     "prompt_number": 7
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='dynamic_binding'></a>\n",
+      "## Dynamic binding and typos in variable names\n",
+      "Be careful, dynamic binding is convenient, but can also quickly become dangerous!"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "print('first list:')\n",
+      "for i in range(3):\n",
+      "    print(i)\n",
+      "    \n",
+      "print('\\nsecond list:')\n",
+      "for j in range(3):\n",
+      "    print(i) # I (intentionally) made typo here!"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "first list:\n",
+        "0\n",
+        "1\n",
+        "2\n",
+        "\n",
+        "second list:\n",
+        "2\n",
+        "2\n",
+        "2\n"
+       ]
+      }
+     ],
+     "prompt_number": 14
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='out_of_range_slicing'></a>\n",
+      "## List slicing using indexes that are \"out of range\""
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "As we have all encountered it 1 (x10000) time(s) in our live, the infamous `IndexError`:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_list = [1, 2, 3, 4, 5]\n",
+      "print(my_list[5])"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "ename": "IndexError",
+       "evalue": "list index out of range",
+       "output_type": "pyerr",
+       "traceback": [
+        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mIndexError\u001b[0m                                Traceback (most recent call last)",
+        "\u001b[0;32m<ipython-input-15-eb273dc36fdc>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0mmy_list\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m2\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m3\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m4\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m5\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmy_list\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m5\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+        "\u001b[0;31mIndexError\u001b[0m: list index out of range"
+       ]
+      }
+     ],
+     "prompt_number": 15
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "But suprisingly, it is not raised when we are doing list slicing, which can be a really pain for debugging:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_list = [1, 2, 3, 4, 5]\n",
+      "print(my_list[5:])"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "[]\n"
+       ]
+      }
+     ],
+     "prompt_number": 16
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='unboundlocalerror'></a>\n",
+      "## Reusing global variable names and `UnboundLocalErrors`"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Usually, it is no problem to access global variables in the local scope of a function:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    print(var)\n",
+      "\n",
+      "var = 'global'\n",
+      "my_func()"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "global\n"
+       ]
+      }
+     ],
+     "prompt_number": 37
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "And is also no problem to use the same variable name in the local scope without affecting the local counterpart: "
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    var = 'locally changed'\n",
+      "\n",
+      "var = 'global'\n",
+      "my_func()\n",
+      "print(var)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "global\n"
+       ]
+      }
+     ],
+     "prompt_number": 38
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "But we have to be careful if we use a variable name that occurs in the global scope, and we want to access it in the local function scope if we want to reuse this name:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    print(var) # want to access global variable\n",
+      "    var = 'locally changed' # but Python thinks we forgot to define the local variable!\n",
+      "    \n",
+      "var = 'global'\n",
+      "my_func()"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "ename": "UnboundLocalError",
+       "evalue": "local variable 'var' referenced before assignment",
+       "output_type": "pyerr",
+       "traceback": [
+        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mUnboundLocalError\u001b[0m                         Traceback (most recent call last)",
+        "\u001b[0;32m<ipython-input-40-3afd870b7c35>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[0mvar\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m'global'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 6\u001b[0;31m \u001b[0mmy_func\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+        "\u001b[0;32m<ipython-input-40-3afd870b7c35>\u001b[0m in \u001b[0;36mmy_func\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0mmy_func\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m     \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mvar\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# want to access global variable\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      3\u001b[0m     \u001b[0mvar\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m'locally changed'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[0mvar\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m'global'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
+        "\u001b[0;31mUnboundLocalError\u001b[0m: local variable 'var' referenced before assignment"
+       ]
+      }
+     ],
+     "prompt_number": 40
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "In this case, we have to use the `global` keyword!"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    global var\n",
+      "    print(var) # want to access global variable\n",
+      "    var = 'locally changed' # changes the gobal variable\n",
+      "\n",
+      "var = 'global'\n",
+      "\n",
+      "my_func()\n",
+      "print(var)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "global\n",
+        "locally changed\n"
+       ]
+      }
+     ],
+     "prompt_number": 43
+    },
     {
      "cell_type": "code",
      "collapsed": false,
diff --git a/not_so_obvious_python_stuff.ipynb b/not_so_obvious_python_stuff.ipynb
index 03255fd..3678a4e 100644
--- a/not_so_obvious_python_stuff.ipynb
+++ b/not_so_obvious_python_stuff.ipynb
@@ -1,7 +1,7 @@
 {
  "metadata": {
   "name": "",
-  "signature": "sha256:02c6c63beb1de9373d69615a4ba37640a7b01c8f2d088dbfaa84bdaf3452f1c5"
+  "signature": "sha256:2e4322ee7bffc6746194af4b3ac6bb9cd8794c14bea2575e3097821a7d5f9b52"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -64,7 +64,10 @@
       "- [When mutable contents of immutable tuples aren't so mutable](#immutable_tuple)\n",
       "- [List comprehensions are fast, but generators are faster!?](#list_generator)\n",
       "- [Public vs. private class methods and name mangling](#private_class)\n",
-      "- [The consequences of modifying a list when looping through it](#looping_pitfall)"
+      "- [The consequences of modifying a list when looping through it](#looping_pitfall)\n",
+      "- [Dynamic binding and typos in variable names](#dynamic_binding)\n",
+      "- [List slicing using indexes that are \"out of range](#out_of_range_slicing)\n",
+      "- [Reusing global variable names and UnboundLocalErrors](#unboundlocalerror)"
      ]
     },
     {
@@ -516,7 +519,7 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "Don't use mutable objects (e.g., dictionaries, lists, sets, etc.) as default arguments for functions! You might expect that a new list is created every time when we call the function without providing an argument for the default parameter, but this is not the case: Python will create the mutable object (default parameter) the first time the function is defined - not when it is called, see the following code:\n",
+      "Don't use mutable objects (e.g., dictionaries, lists, sets, etc.) as default arguments for functions! You might expect that a new list is created every time when we call the function without providing an argument for the default parameter, but this is not the case: **Python will create the mutable object (default parameter) the first time the function is defined - not when it is called**, see the following code:\n",
       "\n",
       "(Original source: [http://docs.python-guide.org/en/latest/writing/gotchas/](http://docs.python-guide.org/en/latest/writing/gotchas/)"
      ]
@@ -549,6 +552,48 @@
      ],
      "prompt_number": 1
     },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Another good example showing that demonstrates that default arguments are created when the function is created (**and not when it is called!**):"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "import time\n",
+      "def report_arg(my_default=time.time()):\n",
+      "    print(my_default)\n",
+      "\n",
+      "report_arg()\n",
+      "\n",
+      "time.sleep(5)\n",
+      "\n",
+      "report_arg()"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "1397764090.456688\n",
+        "1397764090.456688"
+       ]
+      },
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "\n"
+       ]
+      }
+     ],
+     "prompt_number": 10
+    },
     {
      "cell_type": "markdown",
      "metadata": {},
@@ -1314,7 +1359,8 @@
      "cell_type": "markdown",
      "metadata": {},
      "source": [
-      "It can be really dangerous to modify a list when iterating through - it is a very common pitfall that can cause unintended behavour!"
+      "It can be really dangerous to modify a list when iterating through - it is a very common pitfall that can cause unintended behavior!  \n",
+      "Look at the following examples, and for a fun exercise: try to figure out what is going on before you skip to the solution!"
      ]
     },
     {
@@ -1398,6 +1444,266 @@
       }
      ],
      "prompt_number": 7
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='dynamic_binding'></a>\n",
+      "## Dynamic binding and typos in variable names\n",
+      "Be careful, dynamic binding is convenient, but can also quickly become dangerous!"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "print('first list:')\n",
+      "for i in range(3):\n",
+      "    print(i)\n",
+      "    \n",
+      "print('\\nsecond list:')\n",
+      "for j in range(3):\n",
+      "    print(i) # I (intentionally) made typo here!"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "first list:\n",
+        "0\n",
+        "1\n",
+        "2\n",
+        "\n",
+        "second list:\n",
+        "2\n",
+        "2\n",
+        "2\n"
+       ]
+      }
+     ],
+     "prompt_number": 14
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='out_of_range_slicing'></a>\n",
+      "## List slicing using indexes that are \"out of range\""
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "As we have all encountered it 1 (x10000) time(s) in our live, the infamous `IndexError`:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_list = [1, 2, 3, 4, 5]\n",
+      "print(my_list[5])"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "ename": "IndexError",
+       "evalue": "list index out of range",
+       "output_type": "pyerr",
+       "traceback": [
+        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mIndexError\u001b[0m                                Traceback (most recent call last)",
+        "\u001b[0;32m<ipython-input-15-eb273dc36fdc>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0mmy_list\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m[\u001b[0m\u001b[0;36m1\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m2\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m3\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m4\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;36m5\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmy_list\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m5\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+        "\u001b[0;31mIndexError\u001b[0m: list index out of range"
+       ]
+      }
+     ],
+     "prompt_number": 15
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "But suprisingly, it is not raised when we are doing list slicing, which can be a really pain for debugging:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "my_list = [1, 2, 3, 4, 5]\n",
+      "print(my_list[5:])"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "[]\n"
+       ]
+      }
+     ],
+     "prompt_number": 16
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "<br>\n",
+      "<br>\n",
+      "<a name='unboundlocalerror'></a>\n",
+      "## Reusing global variable names and `UnboundLocalErrors`"
+     ]
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "Usually, it is no problem to access global variables in the local scope of a function:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    print(var)\n",
+      "\n",
+      "var = 'global'\n",
+      "my_func()"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "global\n"
+       ]
+      }
+     ],
+     "prompt_number": 37
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "And is also no problem to use the same variable name in the local scope without affecting the local counterpart: "
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    var = 'locally changed'\n",
+      "\n",
+      "var = 'global'\n",
+      "my_func()\n",
+      "print(var)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "global\n"
+       ]
+      }
+     ],
+     "prompt_number": 38
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "But we have to be careful if we use a variable name that occurs in the global scope, and we want to access it in the local function scope if we want to reuse this name:"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    print(var) # want to access global variable\n",
+      "    var = 'locally changed' # but Python thinks we forgot to define the local variable!\n",
+      "    \n",
+      "var = 'global'\n",
+      "my_func()"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "ename": "UnboundLocalError",
+       "evalue": "local variable 'var' referenced before assignment",
+       "output_type": "pyerr",
+       "traceback": [
+        "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m\n\u001b[0;31mUnboundLocalError\u001b[0m                         Traceback (most recent call last)",
+        "\u001b[0;32m<ipython-input-40-3afd870b7c35>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[0mvar\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m'global'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 6\u001b[0;31m \u001b[0mmy_func\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+        "\u001b[0;32m<ipython-input-40-3afd870b7c35>\u001b[0m in \u001b[0;36mmy_func\u001b[0;34m()\u001b[0m\n\u001b[1;32m      1\u001b[0m \u001b[0;32mdef\u001b[0m \u001b[0mmy_func\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m----> 2\u001b[0;31m     \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mvar\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;31m# want to access global variable\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m      3\u001b[0m     \u001b[0mvar\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m'locally changed'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      4\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m      5\u001b[0m \u001b[0mvar\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34m'global'\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
+        "\u001b[0;31mUnboundLocalError\u001b[0m: local variable 'var' referenced before assignment"
+       ]
+      }
+     ],
+     "prompt_number": 40
+    },
+    {
+     "cell_type": "markdown",
+     "metadata": {},
+     "source": [
+      "In this case, we have to use the `global` keyword!"
+     ]
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [
+      "def my_func():\n",
+      "    global var\n",
+      "    print(var) # want to access global variable\n",
+      "    var = 'locally changed' # changes the gobal variable\n",
+      "\n",
+      "var = 'global'\n",
+      "\n",
+      "my_func()\n",
+      "print(var)"
+     ],
+     "language": "python",
+     "metadata": {},
+     "outputs": [
+      {
+       "output_type": "stream",
+       "stream": "stdout",
+       "text": [
+        "global\n",
+        "locally changed\n"
+       ]
+      }
+     ],
+     "prompt_number": 43
+    },
+    {
+     "cell_type": "code",
+     "collapsed": false,
+     "input": [],
+     "language": "python",
+     "metadata": {},
+     "outputs": []
     }
    ],
    "metadata": {}