Improve formatting, add example using nonlocal, improve coroutine

Author: gjbex

source-code/functional-programming/functional_programming_style.ipynb

@@ -4,14 +4,25 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "# Functional programming style"
+    "# Requirements"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from collections import Counter\n",
+    "from functools import reduce, partial\n",
+    "import random"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Applying function to iterables"
+    "# Applying function to iterables"
    ]
   },
   {
@@ -35,12 +46,18 @@
     }
    ],
    "source": [
-    "import random\n",
     "l1 = list(range(10))\n",
     "l2 = random.choices(range(3), k=7)\n",
     "print(l1, l2)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## map"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -84,6 +101,13 @@
     "Note that the result of `map` is not a list, but rather an iterator, even when it is appllied to a list."
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## filter"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -115,17 +139,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Python has quite number of reduction functions such as `sum`, `max`, and `min`, however, using the `reduce` function in `functools` we can easily write our own."
+    "## reduce"
    ]
   },
   {
-   "cell_type": "code",
-   "execution_count": 4,
+   "cell_type": "markdown",
    "metadata": {},
-   "outputs": [],
    "source": [
-    "from collections import Counter\n",
-    "from functools import reduce"
+    "Python has quite number of reduction functions such as `sum`, `max`, and `min`, however, using the `reduce` function in `functools` we can easily write our own."
    ]
   },
   {
@@ -208,7 +229,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Higher order functions"
+    "# Higher order functions"
    ]
   },
   {
@@ -218,15 +239,6 @@
     "A new function can be created out of an existing function using `partial` to fix values for one or more arguments of the original function."
    ]
   },
-  {
-   "cell_type": "code",
-   "execution_count": 9,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "from functools import partial"
-   ]
-  },
   {
    "cell_type": "code",
    "execution_count": 10,
@@ -318,7 +330,70 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Coroutines"
+    "Closures can also be used to accumulate data.  The following closure will generate a function that returns a value that is incremented by one on each invocation."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def create_counter():\n",
+    "    n = 0\n",
+    "    def counter():\n",
+    "        nonlocal n\n",
+    "        n += 1\n",
+    "        return n\n",
+    "    return counter"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "c1, c2 = create_counter(), create_counter()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "1\n",
+      "2\n",
+      "3\n",
+      "4 1\n",
+      "5 2\n",
+      "6 3\n"
+     ]
+    }
+   ],
+   "source": [
+    "for _ in range(3):\n",
+    "    print(c1())\n",
+    "for _ in range(3):\n",
+    "    print(c1(), c2())"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "`nonlocal` ensures that the `n` in outer scope is used, i.e., the variable `n` defined in the generating function `create_counter`."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Coroutines"
    ]
   },
   {
@@ -337,59 +412,65 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 24,
    "metadata": {},
    "outputs": [],
    "source": [
     "def create_elevator(highest_floor):\n",
     "    def elevator():\n",
-    "        floor = 0\n",
+    "        prev_floor = None\n",
+    "        curr_floor = 0\n",
     "        while True:\n",
-    "            next_floor = (yield f'current floor: {floor}')\n",
+    "            next_floor = (yield f'current floor: {curr_floor}' if prev_floor is None else f'move from {prev_floor} to {curr_floor}')\n",
     "            if next_floor is not None:\n",
-    "                if 0 <= next_floor <= highest_floor:\n",
-    "                    floor = next_floor\n",
+    "                if -1 <= next_floor <= highest_floor:\n",
+    "                    prev_floor = curr_floor\n",
+    "                    curr_floor = next_floor\n",
     "                else:\n",
     "                    print(f'no such floor: {next_floor}')\n",
     "            else:\n",
     "                break\n",
     "    my_elevator = elevator()\n",
-    "    next(my_elevator)\n",
+    "    print(next(my_elevator))\n",
     "    return my_elevator    "
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 25,
    "metadata": {},
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "current floor: 0\n"
+     ]
+    }
+   ],
    "source": [
-    "my_elevator = create_elevator(2)"
+    "my_elevator = create_elevator(3)"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 26,
    "metadata": {},
    "outputs": [
     {
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "no such floor: -1\n",
-      "press -1: current floor: 0\n",
-      "press 1: current floor: 1\n",
-      "press 2: current floor: 2\n",
-      "no such floor: 3\n",
-      "press 3: current floor: 2\n",
-      "press 2: current floor: 2\n",
-      "press 0: current floor: 0\n",
-      "no such floor: 3\n",
-      "press 3: current floor: 0\n",
-      "press 1: current floor: 1\n",
-      "press 1: current floor: 1\n",
-      "no such floor: -1\n",
-      "press -1: current floor: 1\n"
+      "press 0: move from 0 to 0\n",
+      "press -1: move from 0 to -1\n",
+      "press 1: move from -1 to 1\n",
+      "press 3: move from 1 to 3\n",
+      "press 3: move from 3 to 3\n",
+      "press 1: move from 3 to 1\n",
+      "press 0: move from 1 to 0\n",
+      "press 3: move from 0 to 3\n",
+      "press -1: move from 3 to -1\n",
+      "press 0: move from -1 to 0\n"
      ]
     }
    ],
@@ -415,7 +496,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.7.5"
+   "version": "3.9.5"
   }
  },
  "nbformat": 4,