|
| 1 | +{ |
| 2 | + "cells": [ |
| 3 | + { |
| 4 | + "cell_type": "markdown", |
| 5 | + "metadata": {}, |
| 6 | + "source": [ |
| 7 | + "# enumerate(iterable, start=0)\n", |
| 8 | + "\n", |
| 9 | + "`iterable` must be a sequence, an iterator, or some other object which **supports iteration**. The `__next__()` method of the iterator returned by `enumerate()` **returns a tuple containing a count (from start which defaults to 0) and the values obtained from iterating over iterable**." |
| 10 | + ] |
| 11 | + }, |
| 12 | + { |
| 13 | + "cell_type": "markdown", |
| 14 | + "metadata": {}, |
| 15 | + "source": [ |
| 16 | + "If you've ever wanted to keep track of both index and value when manipulating a list,\n", |
| 17 | + "you probably did something like this:" |
| 18 | + ] |
| 19 | + }, |
| 20 | + { |
| 21 | + "cell_type": "code", |
| 22 | + "execution_count": 7, |
| 23 | + "metadata": {}, |
| 24 | + "outputs": [ |
| 25 | + { |
| 26 | + "name": "stdout", |
| 27 | + "output_type": "stream", |
| 28 | + "text": [ |
| 29 | + "The 0th fibonacci number is 1.\n", |
| 30 | + "The 1th fibonacci number is 1.\n", |
| 31 | + "The 2th fibonacci number is 2.\n", |
| 32 | + "The 3th fibonacci number is 3.\n", |
| 33 | + "The 4th fibonacci number is 5.\n", |
| 34 | + "The 5th fibonacci number is 8.\n", |
| 35 | + "The 6th fibonacci number is 13.\n", |
| 36 | + "The 7th fibonacci number is 21.\n" |
| 37 | + ] |
| 38 | + } |
| 39 | + ], |
| 40 | + "source": [ |
| 41 | + "fibonacci = [1, 1, 2, 3, 5, 8, 13, 21]\n", |
| 42 | + "for i in range(len(fibonacci)):\n", |
| 43 | + " print(\"The {}th fibonacci number is {}.\".format(i, fibonacci[i]))" |
| 44 | + ] |
| 45 | + }, |
| 46 | + { |
| 47 | + "cell_type": "markdown", |
| 48 | + "metadata": {}, |
| 49 | + "source": [ |
| 50 | + "But if we wanted to start counting from 1 or something, we would need to do:" |
| 51 | + ] |
| 52 | + }, |
| 53 | + { |
| 54 | + "cell_type": "code", |
| 55 | + "execution_count": 8, |
| 56 | + "metadata": {}, |
| 57 | + "outputs": [ |
| 58 | + { |
| 59 | + "name": "stdout", |
| 60 | + "output_type": "stream", |
| 61 | + "text": [ |
| 62 | + "The 1th fibonacci number is 1.\n", |
| 63 | + "The 2th fibonacci number is 1.\n", |
| 64 | + "The 3th fibonacci number is 2.\n", |
| 65 | + "The 4th fibonacci number is 3.\n", |
| 66 | + "The 5th fibonacci number is 5.\n", |
| 67 | + "The 6th fibonacci number is 8.\n", |
| 68 | + "The 7th fibonacci number is 13.\n", |
| 69 | + "The 8th fibonacci number is 21.\n" |
| 70 | + ] |
| 71 | + } |
| 72 | + ], |
| 73 | + "source": [ |
| 74 | + "fibonacci = [1, 1, 2, 3, 5, 8, 13, 21]\n", |
| 75 | + "for i in range(len(fibonacci)):\n", |
| 76 | + " print(\"The {}th fibonacci number is {}.\".format(i+1, fibonacci[i]))" |
| 77 | + ] |
| 78 | + }, |
| 79 | + { |
| 80 | + "cell_type": "markdown", |
| 81 | + "metadata": {}, |
| 82 | + "source": [ |
| 83 | + "You can achieve the same results using the `enumerate()` function, but you instead get\n", |
| 84 | + "separate variables for your index and element, so it's a bit easier to read." |
| 85 | + ] |
| 86 | + }, |
| 87 | + { |
| 88 | + "cell_type": "code", |
| 89 | + "execution_count": 9, |
| 90 | + "metadata": {}, |
| 91 | + "outputs": [ |
| 92 | + { |
| 93 | + "name": "stdout", |
| 94 | + "output_type": "stream", |
| 95 | + "text": [ |
| 96 | + "The 0th fibonacci number is 1.\n", |
| 97 | + "The 1th fibonacci number is 1.\n", |
| 98 | + "The 2th fibonacci number is 2.\n", |
| 99 | + "The 3th fibonacci number is 3.\n", |
| 100 | + "The 4th fibonacci number is 5.\n", |
| 101 | + "The 5th fibonacci number is 8.\n", |
| 102 | + "The 6th fibonacci number is 13.\n", |
| 103 | + "The 7th fibonacci number is 21.\n" |
| 104 | + ] |
| 105 | + } |
| 106 | + ], |
| 107 | + "source": [ |
| 108 | + "fibonacci = [1, 1, 2, 3, 5, 8, 13, 21]\n", |
| 109 | + "\n", |
| 110 | + "for index, number in enumerate(fibonacci):\n", |
| 111 | + " print(\"The {}th fibonacci number is {}.\".format(index, number))" |
| 112 | + ] |
| 113 | + }, |
| 114 | + { |
| 115 | + "cell_type": "markdown", |
| 116 | + "metadata": {}, |
| 117 | + "source": [ |
| 118 | + "In more difficult problems, referring to `i+1`for counting, but using index `i`, could get confusing since \n", |
| 119 | + "they don't match. In this scenario, the `enumerate()` function gives us a little more flexibility since\n", |
| 120 | + "we can specify any `start` that we want:" |
| 121 | + ] |
| 122 | + }, |
| 123 | + { |
| 124 | + "cell_type": "code", |
| 125 | + "execution_count": 10, |
| 126 | + "metadata": {}, |
| 127 | + "outputs": [ |
| 128 | + { |
| 129 | + "name": "stdout", |
| 130 | + "output_type": "stream", |
| 131 | + "text": [ |
| 132 | + "The 1th fibonacci number is 1.\n", |
| 133 | + "The 2th fibonacci number is 1.\n", |
| 134 | + "The 3th fibonacci number is 2.\n", |
| 135 | + "The 4th fibonacci number is 3.\n", |
| 136 | + "The 5th fibonacci number is 5.\n", |
| 137 | + "The 6th fibonacci number is 8.\n", |
| 138 | + "The 7th fibonacci number is 13.\n", |
| 139 | + "The 8th fibonacci number is 21.\n" |
| 140 | + ] |
| 141 | + } |
| 142 | + ], |
| 143 | + "source": [ |
| 144 | + "fibonacci = [1, 1, 2, 3, 5, 8, 13, 21]\n", |
| 145 | + "\n", |
| 146 | + "for index, number in enumerate(fibonacci, start=1):\n", |
| 147 | + " print(\"The {}th fibonacci number is {}.\".format(index, number))" |
| 148 | + ] |
| 149 | + } |
| 150 | + ], |
| 151 | + "metadata": { |
| 152 | + "kernelspec": { |
| 153 | + "display_name": "Python 3", |
| 154 | + "language": "python", |
| 155 | + "name": "python3" |
| 156 | + }, |
| 157 | + "language_info": { |
| 158 | + "codemirror_mode": { |
| 159 | + "name": "ipython", |
| 160 | + "version": 3 |
| 161 | + }, |
| 162 | + "file_extension": ".py", |
| 163 | + "mimetype": "text/x-python", |
| 164 | + "name": "python", |
| 165 | + "nbconvert_exporter": "python", |
| 166 | + "pygments_lexer": "ipython3", |
| 167 | + "version": "3.6.4" |
| 168 | + } |
| 169 | + }, |
| 170 | + "nbformat": 4, |
| 171 | + "nbformat_minor": 2 |
| 172 | +} |
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