|
| 1 | +{ |
| 2 | + "cells": [ |
| 3 | + { |
| 4 | + "cell_type": "markdown", |
| 5 | + "metadata": {}, |
| 6 | + "source": [ |
| 7 | + "# Python List Iteration\n", |
| 8 | + "A variety of ways to iterate Lists, including for loop, while loop, enumerate." |
| 9 | + ] |
| 10 | + }, |
| 11 | + { |
| 12 | + "cell_type": "markdown", |
| 13 | + "metadata": {}, |
| 14 | + "source": [ |
| 15 | + "----\n", |
| 16 | + "The standard for loop works great if inside the loop you only need the item and not its index." |
| 17 | + ] |
| 18 | + }, |
| 19 | + { |
| 20 | + "cell_type": "code", |
| 21 | + "execution_count": 1, |
| 22 | + "metadata": {}, |
| 23 | + "outputs": [ |
| 24 | + { |
| 25 | + "name": "stdout", |
| 26 | + "output_type": "stream", |
| 27 | + "text": [ |
| 28 | + "a\n", |
| 29 | + "b\n", |
| 30 | + "c\n", |
| 31 | + "d\n", |
| 32 | + "e\n" |
| 33 | + ] |
| 34 | + } |
| 35 | + ], |
| 36 | + "source": [ |
| 37 | + "letters = ['a', 'b', 'c', 'd', 'e']\n", |
| 38 | + "\n", |
| 39 | + "for letter in letters:\n", |
| 40 | + " print(letter)" |
| 41 | + ] |
| 42 | + }, |
| 43 | + { |
| 44 | + "cell_type": "markdown", |
| 45 | + "metadata": {}, |
| 46 | + "source": [ |
| 47 | + "----\n", |
| 48 | + "If you need the index inside the loop you can use range(len(list)). \n", |
| 49 | + "Then you can always get the list item if needed by using the index." |
| 50 | + ] |
| 51 | + }, |
| 52 | + { |
| 53 | + "cell_type": "code", |
| 54 | + "execution_count": 2, |
| 55 | + "metadata": {}, |
| 56 | + "outputs": [ |
| 57 | + { |
| 58 | + "name": "stdout", |
| 59 | + "output_type": "stream", |
| 60 | + "text": [ |
| 61 | + "letters 0 = a\n", |
| 62 | + "letters 1 = b\n", |
| 63 | + "letters 2 = c\n", |
| 64 | + "letters 3 = d\n", |
| 65 | + "letters 4 = e\n" |
| 66 | + ] |
| 67 | + } |
| 68 | + ], |
| 69 | + "source": [ |
| 70 | + "for index in range(len(letters)):\n", |
| 71 | + " print('letters', index, '=', letters[index])" |
| 72 | + ] |
| 73 | + }, |
| 74 | + { |
| 75 | + "cell_type": "markdown", |
| 76 | + "metadata": {}, |
| 77 | + "source": [ |
| 78 | + "----\n", |
| 79 | + "Best option if you need both index and item inside the loop is to use Python's **enumerate** function. \n", |
| 80 | + "Enumerate works in both Python 2.x and 3.x" |
| 81 | + ] |
| 82 | + }, |
| 83 | + { |
| 84 | + "cell_type": "code", |
| 85 | + "execution_count": 3, |
| 86 | + "metadata": {}, |
| 87 | + "outputs": [ |
| 88 | + { |
| 89 | + "name": "stdout", |
| 90 | + "output_type": "stream", |
| 91 | + "text": [ |
| 92 | + "letters 0 = a\n", |
| 93 | + "letters 1 = b\n", |
| 94 | + "letters 2 = c\n", |
| 95 | + "letters 3 = d\n", |
| 96 | + "letters 4 = e\n" |
| 97 | + ] |
| 98 | + } |
| 99 | + ], |
| 100 | + "source": [ |
| 101 | + "for index, item in enumerate(letters):\n", |
| 102 | + " print('letters', index, '=', item)" |
| 103 | + ] |
| 104 | + }, |
| 105 | + { |
| 106 | + "cell_type": "markdown", |
| 107 | + "metadata": {}, |
| 108 | + "source": [ |
| 109 | + "Enumerate actually returns an iterable enumerate object, \n", |
| 110 | + "which is a sequence of tuples of (index, item)." |
| 111 | + ] |
| 112 | + }, |
| 113 | + { |
| 114 | + "cell_type": "code", |
| 115 | + "execution_count": 4, |
| 116 | + "metadata": {}, |
| 117 | + "outputs": [ |
| 118 | + { |
| 119 | + "name": "stdout", |
| 120 | + "output_type": "stream", |
| 121 | + "text": [ |
| 122 | + "(0, 'a')\n", |
| 123 | + "(1, 'b')\n", |
| 124 | + "<class 'enumerate'>\n" |
| 125 | + ] |
| 126 | + } |
| 127 | + ], |
| 128 | + "source": [ |
| 129 | + "enum_obj = enumerate(letters)\n", |
| 130 | + "print(next(enum_obj))\n", |
| 131 | + "print(next(enum_obj))\n", |
| 132 | + "print(type(enum_obj))" |
| 133 | + ] |
| 134 | + }, |
| 135 | + { |
| 136 | + "cell_type": "markdown", |
| 137 | + "metadata": {}, |
| 138 | + "source": [ |
| 139 | + "----\n", |
| 140 | + "Probably the clumsiest way to iterate a list in Python -- the **while loop**. \n", |
| 141 | + "Requires index initialization before list, and incrementation inside loop." |
| 142 | + ] |
| 143 | + }, |
| 144 | + { |
| 145 | + "cell_type": "code", |
| 146 | + "execution_count": 5, |
| 147 | + "metadata": {}, |
| 148 | + "outputs": [ |
| 149 | + { |
| 150 | + "name": "stdout", |
| 151 | + "output_type": "stream", |
| 152 | + "text": [ |
| 153 | + "letters 0 = a\n", |
| 154 | + "letters 1 = b\n", |
| 155 | + "letters 2 = c\n", |
| 156 | + "letters 3 = d\n", |
| 157 | + "letters 4 = e\n" |
| 158 | + ] |
| 159 | + } |
| 160 | + ], |
| 161 | + "source": [ |
| 162 | + "index = 0\n", |
| 163 | + "while index < len(letters): \n", |
| 164 | + " print('letters', index, '=', letters[index]) \n", |
| 165 | + " index += 1" |
| 166 | + ] |
| 167 | + }, |
| 168 | + { |
| 169 | + "cell_type": "code", |
| 170 | + "execution_count": null, |
| 171 | + "metadata": {}, |
| 172 | + "outputs": [], |
| 173 | + "source": [] |
| 174 | + } |
| 175 | + ], |
| 176 | + "metadata": { |
| 177 | + "kernelspec": { |
| 178 | + "display_name": "Python 3", |
| 179 | + "language": "python", |
| 180 | + "name": "python3" |
| 181 | + }, |
| 182 | + "language_info": { |
| 183 | + "codemirror_mode": { |
| 184 | + "name": "ipython", |
| 185 | + "version": 3 |
| 186 | + }, |
| 187 | + "file_extension": ".py", |
| 188 | + "mimetype": "text/x-python", |
| 189 | + "name": "python", |
| 190 | + "nbconvert_exporter": "python", |
| 191 | + "pygments_lexer": "ipython3", |
| 192 | + "version": "3.7.0" |
| 193 | + } |
| 194 | + }, |
| 195 | + "nbformat": 4, |
| 196 | + "nbformat_minor": 2 |
| 197 | +} |
0 commit comments