Add flatten example

Author: gjbex

source_code/README.md

@@ -34,3 +34,5 @@ certain subtle points.
    longest chain.
 1. `knights_tour.ipynb`: example of using backtracking to solve the knight's tour
    problem.
+1. `flatten.ipynb`: `itertools.chain` may not flatten a data structure as you might
+   expect or want.

source_code/flatten.ipynb

@@ -0,0 +1,162 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "id": "82480372-c0ad-440c-a076-5e8cc6666e48",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "import itertools"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "2e8c295a-92e9-4ee5-aefa-5ebe658ebc04",
+   "metadata": {},
+   "source": [
+    "Although `itertools.chain` is very useful, it may not do what you intend when elements are strings. It also doesn't recurse beyond the first level."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 8,
+   "id": "5f6e1c01-98e4-4093-984b-2f8b470c804b",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "data = [('a', 'b'), 'c012', ('d', 'e490'), 'f', 'g', (1, (3, 7))]"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 9,
+   "id": "96e0ea2e-28cc-438b-9e5d-e98edc521883",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "a\n",
+      "b\n",
+      "c\n",
+      "0\n",
+      "1\n",
+      "2\n",
+      "d\n",
+      "e490\n",
+      "f\n",
+      "g\n",
+      "1\n",
+      "(3, 7)\n"
+     ]
+    }
+   ],
+   "source": [
+    "for item in itertools.chain(*data):\n",
+    "    print(item)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "id": "308fe429-20ae-41b6-832d-ee840c1a1bb6",
+   "metadata": {},
+   "source": [
+    "The following function may be more what you expect."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 10,
+   "id": "b36d51df-47b6-48a6-b79e-778b5e88e17e",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def flatten(data, recurse=True):\n",
+    "    for item in data:\n",
+    "        if hasattr(item, '__iter__') and not isinstance(item, str):\n",
+    "            for subitem in flatten(item) if recurse else item:\n",
+    "                yield subitem\n",
+    "        else:\n",
+    "            yield item"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 11,
+   "id": "64a64ff7-8b26-462a-b98b-c4c2c69b9014",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "a\n",
+      "b\n",
+      "c012\n",
+      "d\n",
+      "e490\n",
+      "f\n",
+      "g\n",
+      "1\n",
+      "3\n",
+      "7\n"
+     ]
+    }
+   ],
+   "source": [
+    "for item in flatten(data):\n",
+    "    print(item)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "id": "bbb96b04-1e84-4c6d-bd8d-18638732f32e",
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "a\n",
+      "b\n",
+      "c012\n",
+      "d\n",
+      "e490\n",
+      "f\n",
+      "g\n",
+      "1\n",
+      "(3, 7)\n"
+     ]
+    }
+   ],
+   "source": [
+    "for item in flatten(data, recurse=False):\n",
+    "    print(item)"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3 (ipykernel)",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.11.3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}