{
"cells": [
{
"cell_type": "markdown",
"id": "e7e19e44",
"metadata": {},
"source": [
"# 元组"
]
},
{
"cell_type": "markdown",
"id": "6b387a2b",
"metadata": {},
"source": [
"## 基本操作"
]
},
{
"cell_type": "markdown",
"id": "8f9d2a64",
"metadata": {},
"source": [
"与列表类似，元组是一个有序序列，但是不可变。\n",
"\n",
"元组用小括号`()`生成："
]
},
{
"cell_type": "code",
"execution_count": 1,
"id": "35ee8cf4",
"metadata": {},
"outputs": [],
"source": [
"t = (10, 11, 12, 13, 14)"
]
},
{
"cell_type": "code",
"execution_count": 2,
"id": "c84434ff",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"(10, 11, 12, 13, 14)"
]
},
"execution_count": 2,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"t"
]
},
{
"cell_type": "markdown",
"id": "adeda902",
"metadata": {},
"source": [
"可以索引，切片："
]
},
{
"cell_type": "code",
"execution_count": 3,
"id": "af7e51ec",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"10"
]
},
"execution_count": 3,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"t[0]"
]
},
{
"cell_type": "code",
"execution_count": 4,
"id": "0f0426de",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"(11, 12)"
]
},
"execution_count": 4,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"t[1:3]"
]
},
{
"cell_type": "markdown",
"id": "50e2275b",
"metadata": {},
"source": [
"元组是不可变的，不能通过赋值改变："
]
},
{
"cell_type": "code",
"execution_count": 5,
"id": "979e1f96",
"metadata": {},
"outputs": [
{
"ename": "TypeError",
"evalue": "'tuple' object does not support item assignment",
"output_type": "error",
"traceback": [
"\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[0;31mTypeError\u001b[0m Traceback (most recent call last)",
"Input \u001b[0;32mIn [5]\u001b[0m, in \u001b[0;36m<cell line: 1>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0m t[\u001b[38;5;241m0\u001b[39m] \u001b[38;5;241m=\u001b[39m \u001b[38;5;241m1\u001b[39m\n",
"\u001b[0;31mTypeError\u001b[0m: 'tuple' object does not support item assignment"
]
}
],
"source": [
"t[0] = 1"
]
},
{
"cell_type": "markdown",
"id": "1625a74f",
"metadata": {},
"source": [
"## 单元素的元组生成\n",
"\n",
"由于()在表达式中被应用，只含有单个元素的元组容易和表达式混淆，所以采用下列方式定义只有一个元素的元组："
]
},
{
"cell_type": "code",
"execution_count": 6,
"id": "ca547219",
"metadata": {},
"outputs": [],
"source": [
"a = (10)"
]
},
{
"cell_type": "code",
"execution_count": 7,
"id": "71eb0d2b",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"10"
]
},
"execution_count": 7,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a"
]
},
{
"cell_type": "code",
"execution_count": 8,
"id": "8866d98d",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"int"
]
},
"execution_count": 8,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"type(a)"
]
},
{
"cell_type": "code",
"execution_count": 9,
"id": "1a4e83a9",
"metadata": {},
"outputs": [],
"source": [
"a = (10,)"
]
},
{
"cell_type": "code",
"execution_count": 10,
"id": "9c00526f",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"(10,)"
]
},
"execution_count": 10,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a"
]
},
{
"cell_type": "code",
"execution_count": 11,
"id": "d8e52d8f",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"tuple"
]
},
"execution_count": 11,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"type(a)"
]
},
{
"cell_type": "markdown",
"id": "46100c0e",
"metadata": {},
"source": [
"## 列表与元组的转换\n",
"\n",
"用构造方法`list`和`tuple`可以相互转换："
]
},
{
"cell_type": "code",
"execution_count": 12,
"id": "f7d0a973",
"metadata": {},
"outputs": [],
"source": [
"a = [10, 11, 12, 13, 14]"
]
},
{
"cell_type": "code",
"execution_count": 13,
"id": "1a1c628d",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"(10, 11, 12, 13, 14)"
]
},
"execution_count": 13,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"tuple(a)"
]
},
{
"cell_type": "code",
"execution_count": 14,
"id": "b53b3230",
"metadata": {},
"outputs": [],
"source": [
"a = (10, 11, 12, 13, 14)"
]
},
{
"cell_type": "code",
"execution_count": 15,
"id": "c6d4da04",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"[10, 11, 12, 13, 14]"
]
},
"execution_count": 15,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"list(a)"
]
},
{
"cell_type": "markdown",
"id": "ba4a8d6a",
"metadata": {},
"source": [
"## 元组方法\n",
"\n",
"由于元组是不可变的，所以只能有一些不可变自身的方法，例如计算元素个数`.count()`方法和元素位置`.index()`方法，用法与列表一样："
]
},
{
"cell_type": "code",
"execution_count": 16,
"id": "d0962bc0",
"metadata": {},
"outputs": [],
"source": [
"a = (10, 11, 12, 13, 14)"
]
},
{
"cell_type": "code",
"execution_count": 17,
"id": "04681a99",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"1"
]
},
"execution_count": 17,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a.count(10)"
]
},
{
"cell_type": "code",
"execution_count": 18,
"id": "aa075db7",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"2"
]
},
"execution_count": 18,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a.index(12)"
]
},
{
"cell_type": "markdown",
"id": "c6ab6f06",
"metadata": {},
"source": [
"## 列表与元组的速度比较\n",
"\n",
"IPython 中用 `magic` 命令 `%timeit` 来计时。\n",
"\n",
"比较列表与元组的生成速度："
]
},
{
"cell_type": "code",
"execution_count": 19,
"id": "4f09ce16",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"108 ns ± 5.29 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)\n"
]
}
],
"source": [
"%timeit -n 100000 [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]"
]
},
{
"cell_type": "code",
"execution_count": 20,
"id": "0d7a5477",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"12.7 ns ± 2.44 ns per loop (mean ± std. dev. of 7 runs, 100,000 loops each)\n"
]
}
],
"source": [
"%timeit -n 100000 (1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25)"
]
},
{
"cell_type": "markdown",
"id": "459912da",
"metadata": {},
"source": [
"在遍历上，元组和列表的速度表现差不多。\n",
"\n",
"产生内容相同的随机列表和元组："
]
},
{
"cell_type": "code",
"execution_count": 21,
"id": "1fb682e4",
"metadata": {},
"outputs": [],
"source": [
"from numpy.random import rand\n",
"\n",
"values = rand(10000,4)\n",
"\n",
"lst = [list(row) for row in values]\n",
"tup = tuple(tuple(row) for row in values)"
]
},
{
"cell_type": "code",
"execution_count": 22,
"id": "e06d2883",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"719 µs ± 52.2 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
]
}
],
"source": [
"%timeit -n 100 for row in lst: tuple(row)"
]
},
{
"cell_type": "code",
"execution_count": 23,
"id": "5a8991fd",
"metadata": {
"scrolled": true
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"514 µs ± 29.8 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
]
}
],
"source": [
"%timeit -n 100 for row in tup: tuple(row)"
]
},
{
"cell_type": "markdown",
"id": "f5b49abc",
"metadata": {},
"source": [
"比较遍历和索引速度："
]
},
{
"cell_type": "code",
"execution_count": 24,
"id": "c41abaaf",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"2.61 ms ± 112 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
]
}
],
"source": [
"%timeit -n 100 for row in lst: a = row[0] + 1"
]
},
{
"cell_type": "code",
"execution_count": 25,
"id": "05d3a527",
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"2.51 ms ± 88.9 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n"
]
}
],
"source": [
"%timeit for row in tup: a = row[0] + 1"
]
},
{
"cell_type": "markdown",
"id": "0ae5c8dd",
"metadata": {},
"source": [
"总结：元组的生成速度会比列表快很多，迭代速度快一点，索引速度差不多。"
]
},
{
"attachments": {},
"cell_type": "markdown",
"id": "4943884e",
"metadata": {},
"source": [
"## 元组与多变量赋值\n",
"\n",
"Python支持多变量赋值的模式："
]
},
{
"cell_type": "code",
"execution_count": 26,
"id": "2ecf3911",
"metadata": {},
"outputs": [],
"source": [
"a, b = 1, 2"
]
},
{
"cell_type": "code",
"execution_count": 27,
"id": "b43b3251",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"1"
]
},
"execution_count": 27,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a"
]
},
{
"cell_type": "code",
"execution_count": 28,
"id": "65c8cc66",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"2"
]
},
"execution_count": 28,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"b"
]
},
{
"cell_type": "markdown",
"id": "75df719f",
"metadata": {},
"source": [
"Python中的多变量赋值，本质是两个元组中的元素进行一一对应，此时，等号两边的元素数目必须相等。例如，将包含两个元素的元组t的值分别赋给a和b："
]
},
{
"cell_type": "code",
"execution_count": 29,
"id": "28a23af1",
"metadata": {},
"outputs": [],
"source": [
"t = (1, 2)"
]
},
{
"cell_type": "code",
"execution_count": 30,
"id": "2cf6d0bb",
"metadata": {},
"outputs": [],
"source": [
"a, b = t"
]
},
{
"cell_type": "code",
"execution_count": 31,
"id": "a08094b8",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"1"
]
},
"execution_count": 31,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a"
]
},
{
"attachments": {},
"cell_type": "markdown",
"id": "9d72d41e",
"metadata": {},
"source": [
"利用多变量赋值，变量的交换可以用一行代码实现："
]
},
{
"cell_type": "code",
"execution_count": 32,
"id": "8cb7c70b",
"metadata": {},
"outputs": [],
"source": [
"a, b = b, a"
]
},
{
"cell_type": "code",
"execution_count": 33,
"id": "db999b73",
"metadata": {
"scrolled": true
},
"outputs": [
{
"data": {
"text/plain": [
"2"
]
},
"execution_count": 33,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a"
]
},
{
"attachments": {},
"cell_type": "markdown",
"id": "7cb8ac2d",
"metadata": {},
"source": [
"多变量赋值支持超过两个值的操作，只要等号两边的元素数相同："
]
},
{
"cell_type": "code",
"execution_count": 34,
"id": "aa5ebd4f",
"metadata": {},
"outputs": [],
"source": [
"a, b, c = 1, 2, 3"
]
},
{
"cell_type": "markdown",
"id": "8a932b56",
"metadata": {},
"source": [
"嵌套："
]
},
{
"cell_type": "code",
"execution_count": 35,
"id": "5a2b3a03",
"metadata": {},
"outputs": [],
"source": [
"a, (b, c) = 1, (2, 3)"
]
},
{
"cell_type": "markdown",
"id": "10e86d4a",
"metadata": {},
"source": [
"带星号的赋值，将后面的值都变成一个列表给某个变量赋值："
]
},
{
"cell_type": "code",
"execution_count": 36,
"id": "589b4cc8",
"metadata": {},
"outputs": [],
"source": [
"a, *b = 1, 2, 3"
]
},
{
"cell_type": "code",
"execution_count": 37,
"id": "2a65ab3b",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"[2, 3]"
]
},
"execution_count": 37,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"b"
]
},
{
"cell_type": "code",
"execution_count": 38,
"id": "734b13c4",
"metadata": {},
"outputs": [
{
"data": {
"text/plain": [
"1"
]
},
"execution_count": 38,
"metadata": {},
"output_type": "execute_result"
}
],
"source": [
"a"
]
},
{
"cell_type": "code",
"execution_count": null,
"id": "585bab96",
"metadata": {},
"outputs": [],
"source": []
}
],
"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": "3.9.10"
}
},
"nbformat": 4,
"nbformat_minor": 5
}