{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "## 这是list的章节\n", "\n", "\n" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# list\n", "**Python的列表：list。**list是一种有序的集合，可以随时添加和删除其中的元素。\n", "\n", "比如，列出班里所有同学的名字，就可以用一个list表示：\n", "\n" ] }, { "cell_type": "code", "execution_count": 1, "metadata": {}, "outputs": [], "source": [ "classmates = ['Michael', 'Bob', 'Tracy']" ] }, { "cell_type": "code", "execution_count": 2, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Bob', 'Tracy']" ] }, "execution_count": 2, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates" ] }, { "cell_type": "code", "execution_count": 3, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "3" ] }, "execution_count": 3, "metadata": {}, "output_type": "execute_result" } ], "source": [ "# 用len()函数可以获得list元素的个数：\n", "len(classmates)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 一、查\n", "用**索引**访问list中的元素，索引是从$0$开始：" ] }, { "cell_type": "code", "execution_count": 4, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'Michael'" ] }, "execution_count": 4, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates[0]" ] }, { "cell_type": "code", "execution_count": 5, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'Bob'" ] }, "execution_count": 5, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates[1]" ] }, { "cell_type": "code", "execution_count": 6, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'Tracy'" ] }, "execution_count": 6, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates[2]" ] }, { "cell_type": "code", "execution_count": 7, "metadata": {}, "outputs": [ { "ename": "IndexError", "evalue": "list index out of range", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mIndexError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m\u001b[0m\n\u001b[0;32m 1\u001b[0m \u001b[1;31m# 当索引超出了范围时，Python会报一个IndexError错误，所以，要确保索引不要越界，记得最后一个元素的索引是len(classmates) - 1\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[0mclassmates\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m3\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mIndexError\u001b[0m: list index out of range" ] } ], "source": [ "# 当索引超出了范围时，Python会报一个IndexError错误，所以，要确保索引不要越界，记得最后一个元素的索引是len(classmates) - 1\n", "classmates[3]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "如果要**取最后一个元素**，除了计算索引位置外，还可以用$-1$做索引，直接获取最后一个元素：" ] }, { "cell_type": "code", "execution_count": 8, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'Tracy'" ] }, "execution_count": 8, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates[-1]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "取倒数第2个、倒数第3个：" ] }, { "cell_type": "code", "execution_count": 9, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'Bob'" ] }, "execution_count": 9, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates[-2]" ] }, { "cell_type": "code", "execution_count": 10, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'Michael'" ] }, "execution_count": 10, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates[-3]" ] }, { "cell_type": "code", "execution_count": 11, "metadata": {}, "outputs": [ { "ename": "IndexError", "evalue": "list index out of range", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mIndexError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mclassmates\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;33m-\u001b[0m\u001b[1;36m4\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mIndexError\u001b[0m: list index out of range" ] } ], "source": [ "classmates[-4]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "列表和字符串一样可以通过**分片**来查看它的元素" ] }, { "cell_type": "code", "execution_count": 13, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "(10, 16, [12, 14])" ] }, "execution_count": 13, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [10, 11, 12, 13, 14, 15, 16]\n", "a[0],a[-1],a[2:-1:2]" ] }, { "cell_type": "code", "execution_count": 14, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[10, 12, 14, 16]" ] }, "execution_count": 14, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a[::2]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**根据值查index**,列表中某个元素位置" ] }, { "cell_type": "code", "execution_count": 15, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "1" ] }, "execution_count": 15, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [11, 12, 13, 12, 11]\n", "a.index(12)\n", "# a.index(11)" ] }, { "cell_type": "code", "execution_count": null, "metadata": {}, "outputs": [], "source": [] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### in，not in判断从属关系\n", "用 **in** 来看某个元素是否在某个**序列**（不仅仅是列表）中，用**not in**来判断是否不在某个序列中。" ] }, { "cell_type": "code", "execution_count": 16, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "True\n", "False\n" ] } ], "source": [ "a = [10, 11, 12, 13, 14]\n", "print (10 in a)\n", "print (10 not in a)" ] }, { "cell_type": "code", "execution_count": 17, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "True\n", "False\n" ] } ], "source": [ "s = 'hello world'\n", "print ('he' in s)\n", "print ('world' not in s)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 二、增" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**append（）函数，**list是一个可变的有序表，所以，可以往list中**追加元素到末尾**：" ] }, { "cell_type": "code", "execution_count": 18, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Bob', 'Tracy']" ] }, "execution_count": 18, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates" ] }, { "cell_type": "code", "execution_count": 19, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Bob', 'Tracy', 'Adam']" ] }, "execution_count": 19, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates.append('Adam')\n", "classmates" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "可以把元素插入到指定的位置，比如索引号为1的位置：" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**insert()函数**，也可以把元素**插入到指定的位置**，比如索引号为1的位置：" ] }, { "cell_type": "code", "execution_count": 20, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Jack', 'Bob', 'Tracy', 'Adam']" ] }, "execution_count": 20, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates.insert(1, 'Jack')\n", "classmates" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### 向列表添加序列\n", "**extend(lst)方法，** 将序列 lst 的元素依次添加到列表 l 的最后，作用相当于 l += lst。\n" ] }, { "cell_type": "code", "execution_count": 21, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[1, 2, 3, [4, 5]]" ] }, "execution_count": 21, "metadata": {}, "output_type": "execute_result" } ], "source": [ "# 把aa,bb合并，如果用append那么会把bb当作整体插入aa末尾，此时需要使用extend()扩展函数\n", "aa = [1,2,3]\n", "bb = [4,5]\n", "aa.append(bb)\n", "aa" ] }, { "cell_type": "code", "execution_count": 22, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[1, 2, 3, [4, 5], 4, 5]" ] }, "execution_count": 22, "metadata": {}, "output_type": "execute_result" } ], "source": [ "aa+bb" ] }, { "cell_type": "code", "execution_count": 23, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[10, 11, 12, 11, 1, 2]\n" ] } ], "source": [ "a = [10, 11, 12, 11]\n", "a.extend([1, 2]) # 只能有1个参数，扩展后会放在a队列的后面\n", "print (a)" ] }, { "cell_type": "code", "execution_count": 24, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[10, [0, 0], 11, 12, 11, 1, 2]" ] }, "execution_count": 24, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a.insert(1,[0,0])\n", "a" ] }, { "cell_type": "code", "execution_count": 25, "metadata": {}, "outputs": [ { "ename": "TypeError", "evalue": "extend() takes exactly one argument (2 given)", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0ma\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mextend\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;36m2\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;31m#takes exactly one argument (2 given)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mTypeError\u001b[0m: extend() takes exactly one argument (2 given)" ] } ], "source": [ "a.extend(1,[1, 2]) #takes exactly one argument (2 given)" ] }, { "cell_type": "code", "execution_count": 26, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Jack', 'Bob', 'Tracy', 'Adam']" ] }, "execution_count": 26, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 三、删" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**$pop()$函数**，删除list**末尾**的元素" ] }, { "cell_type": "code", "execution_count": 27, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Jack', 'Bob', 'Tracy']" ] }, "execution_count": 27, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates.pop()\n", "classmates" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**$pop(i)$**，删除指定位置的元素，其中i是索引位置：" ] }, { "cell_type": "code", "execution_count": 28, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Bob', 'Tracy']" ] }, "execution_count": 28, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates.pop(1)\n", "classmates" ] }, { "cell_type": "code", "execution_count": 29, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "3" ] }, "execution_count": 29, "metadata": {}, "output_type": "execute_result" } ], "source": [ "[1,2,3].pop()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**删除连续的分片**：" ] }, { "cell_type": "code", "execution_count": 30, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1, 2]\n" ] }, { "data": { "text/plain": [ "[10, 11, 12]" ] }, "execution_count": 30, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [10, 1, 2, 11, 12]\n", "print (a[1:3])\n", "a[1:3] = []\n", "a" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**不连续**（间隔step不为1）的片段进行修改时，两者的元素数目必须一致：" ] }, { "cell_type": "code", "execution_count": 31, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[1, 11, 2, 13, 3]" ] }, "execution_count": 31, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [10, 11, 12, 13, 14]\n", "a[::2] = [1, 2, 3] # 把0，2，4替换为[1，2，3]\n", "# a[::2] = [] # 步长为2，元素个数不一致会报错\n", "a" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**del命令，**:删除**指定位置**的元素" ] }, { "cell_type": "code", "execution_count": 32, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "['a', 'b', 'c']\n" ] } ], "source": [ "a = [1002, 'a', 'b', 'c']\n", "del a[0]\n", "print (a)" ] }, { "cell_type": "code", "execution_count": 33, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[1002]" ] }, "execution_count": 33, "metadata": {}, "output_type": "execute_result" } ], "source": [ "# 删除第1到最后一个元素：\n", "a = [1002, 'a', 'b', 'c']\n", "del a[1:]\n", "a" ] }, { "cell_type": "code", "execution_count": 34, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[1, 2]" ] }, "execution_count": 34, "metadata": {}, "output_type": "execute_result" } ], "source": [ "# 间隔删除元素：\n", "a = ['a', 1, 'b', 2, 'c']\n", "del a[::2]\n", "a" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**remove(ob)方法，按值删除**，会将列表中第一个出现的 ob 删除，如果 ob 不在 l 中会报错。" ] }, { "cell_type": "code", "execution_count": 35, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[10, 12, 13, 11]\n" ] } ], "source": [ "a = [10, 11, 12, 13, 11]\n", "# 移除了第一个 找到的11\n", "a.remove(11)\n", "print (a)" ] }, { "cell_type": "code", "execution_count": 3, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[10, 12, 13]" ] }, "execution_count": 3, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [10, 11, 12, 13, 11]\n", "[i for i in a if i!=11]" ] }, { "cell_type": "code", "execution_count": 4, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[10, 12, 13]" ] }, "execution_count": 4, "metadata": {}, "output_type": "execute_result" } ], "source": [ "for i in a:\n", " if i==11:\n", " a.remove(i)\n", "a" ] }, { "cell_type": "code", "execution_count": 14, "metadata": {}, "outputs": [], "source": [ "a = [10, 11, 12, 13, 11]" ] }, { "cell_type": "code", "execution_count": 15, "metadata": {}, "outputs": [], "source": [ "tem = 11\n", "while tem in a:\n", " a.remove(tem)" ] }, { "cell_type": "code", "execution_count": 16, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[10, 12, 13]" ] }, "execution_count": 16, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 四、改" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "把某个元素**替换**成别的元素，可以直接赋值给对应的索引位置：" ] }, { "cell_type": "code", "execution_count": 36, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Bob', 'Tracy']" ] }, "execution_count": 36, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates" ] }, { "cell_type": "code", "execution_count": 37, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['Michael', 'Sarah', 'Tracy']" ] }, "execution_count": 37, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates[1] = 'Sarah'\n", "classmates" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "list里面的**元素的数据类型**也可以不同：" ] }, { "cell_type": "code", "execution_count": 38, "metadata": {}, "outputs": [], "source": [ "L = ['Apple', 123, True]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**注意：****列表**可以通过索引和分片来修改。但**字符串**，如果我们通过索引或者分片来修改，**Python**会报错：
因为str是不可变对象" ] }, { "cell_type": "code", "execution_count": 39, "metadata": {}, "outputs": [ { "ename": "TypeError", "evalue": "'str' object does not support item assignment", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m\u001b[0m\n\u001b[0;32m 1\u001b[0m \u001b[0ms\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m\"hello world\"\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m 2\u001b[0m \u001b[1;31m# 把开头的 h 改成大写\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[0ms\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m]\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'H'\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mTypeError\u001b[0m: 'str' object does not support item assignment" ] } ], "source": [ "s = \"hello world\"\n", "# 把开头的 h 改成大写\n", "s[0] = 'H'" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "将列表的第2，3两个元素换掉" ] }, { "cell_type": "code", "execution_count": 40, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[10, 1, 2, 13, 14]" ] }, "execution_count": 40, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [10, 11, 12, 13, 14]\n", "a[1:3] = [1, 2] # 索引1，2替换为[1，2]\n", "a" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "对于连续的分片（即步长为 1 ），Python采用的是整段替换的方法，两者的元素个数并不需要相同：" ] }, { "cell_type": "code", "execution_count": 41, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[10, 1, 2, 3, 4, 13, 14]" ] }, "execution_count": 41, "metadata": {}, "output_type": "execute_result" } ], "source": [ "# 例如，将 [11,12] 替换为 [1,2,3,4]\n", "a = [10, 11, 12, 13, 14]\n", "a[1:3] = [1, 2, 3, 4]\n", "a" ] }, { "cell_type": "code", "execution_count": 46, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[1, 11, 2, 13, 3]" ] }, "execution_count": 46, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [10, 11, 12, 13, 14]\n", "a[::2] = [1, 2, 3] \n", "a" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 列表是可变的" ] }, { "cell_type": "code", "execution_count": 42, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[100, 2, 3, 4]\n" ] } ], "source": [ "a = [1, 2, 3, 4]\n", "b = a\n", "b[0] = 100\n", "print(a)" ] }, { "cell_type": "code", "execution_count": null, "metadata": {}, "outputs": [], "source": [] }, { "cell_type": "markdown", "metadata": {}, "source": [ "list元素也可以是另一个list，比如：" ] }, { "cell_type": "code", "execution_count": 48, "metadata": {}, "outputs": [], "source": [ "s = ['python', 'java', ['asp', 'php'], 'scheme']" ] }, { "cell_type": "code", "execution_count": 49, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "4" ] }, "execution_count": 49, "metadata": {}, "output_type": "execute_result" } ], "source": [ "len(s)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "s只有4个元素，其中s[2]又是一个list，拆开写：" ] }, { "cell_type": "code", "execution_count": 50, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "['python', 'java', ['asp', 'php'], 'scheme']" ] }, "execution_count": 50, "metadata": {}, "output_type": "execute_result" } ], "source": [ "p = ['asp', 'php']\n", "s = ['python', 'java', p, 'scheme']\n", "s" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "要拿到'php'可以写$p[1]$或者$s[2][1]$，因此$s$可以看成是一个二维数组，类似的还有三维、四维……数组，不过很少用到。\n", "\n", "如果一个list中一个元素也没有，就是一个空的list，它的长度为$0$：" ] }, { "cell_type": "code", "execution_count": 51, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'asp'" ] }, "execution_count": 51, "metadata": {}, "output_type": "execute_result" } ], "source": [ "s[2][0]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 列表方法" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "1、**count**,列表中某个元素个数" ] }, { "cell_type": "code", "execution_count": 43, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "2" ] }, "execution_count": 43, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [11, 12, 13, 12, 11]\n", "a.count(11)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "2、**sort()方法**， 会将列表中的元素按照一定的规则排序：" ] }, { "cell_type": "code", "execution_count": 44, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1, 2, 10, 11, 11, 13]\n" ] } ], "source": [ "a = [10, 1, 11, 13, 11, 2]\n", "a.sort()\n", "print(a)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ " **3、sorted 函数**,不想改变原来列表中的值，可以使用" ] }, { "cell_type": "code", "execution_count": 45, "metadata": { "scrolled": true }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[10, 1, 11, 13, 11, 2]\n", "[1, 2, 10, 11, 11, 13]\n" ] } ], "source": [ "a = [10, 1, 11, 13, 11, 2]\n", "b = sorted(a)\n", "print (a)\n", "print(b)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**4、reverse()函数,**会将列表中的元素从后向前排列。" ] }, { "cell_type": "code", "execution_count": 46, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "2391151677696\n", "[6, 5, 4, 3, 2, 1]\n", "2391151677696\n" ] } ], "source": [ "a = [1, 2, 3, 4, 5, 6]\n", "print(id(a))\n", "a.reverse()\n", "print (a)\n", "print(id(a))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "如果不想改变原来列表，可以使用这样的方法：" ] }, { "cell_type": "code", "execution_count": 48, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1, 2, 3, 4, 5, 6]\n", "[6, 5, 4, 3, 2, 1]\n", "[6, 5, 4, 3, 2, 1]\n" ] } ], "source": [ "a = [1, 2, 3, 4, 5, 6]\n", "b = a[::-1] # 使用[：：-1]反转\n", "c= a[len(a)-1::-1]\n", "print (a)\n", "print (b)\n", "print (c)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "默认的参数" ] }, { "cell_type": "code", "execution_count": 9, "metadata": {}, "outputs": [], "source": [ "a = [1, 2, 3, 4, 5, 6]" ] }, { "cell_type": "code", "execution_count": 49, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[6, 5, 4, 3, 2, 1]" ] }, "execution_count": 49, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sorted(a,reverse=True)" ] }, { "cell_type": "code", "execution_count": 16, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "[0, 2, 4, 6, 8]" ] }, "execution_count": 16, "metadata": {}, "output_type": "execute_result" } ], "source": [ "list(range(0,9,2))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# tuple\n", "**tuple(元组)**是另一种有序列表。
\n", "tuple和list非常类似，但是tuple一旦初始化就不能修改，比如同样是列出同学的名字:" ] }, { "cell_type": "code", "execution_count": 50, "metadata": {}, "outputs": [], "source": [ "classmates = ('Michael', 'Bob', 'Tracy')" ] }, { "cell_type": "code", "execution_count": 51, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "('Michael', 'Bob', 'Tracy')" ] }, "execution_count": 51, "metadata": {}, "output_type": "execute_result" } ], "source": [ "classmates" ] }, { "cell_type": "code", "execution_count": 52, "metadata": {}, "outputs": [ { "ename": "NameError", "evalue": "name 'cassmates' is not defined", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mNameError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mcassmates\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m=\u001b[0m\u001b[1;34m'Tom'\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mNameError\u001b[0m: name 'cassmates' is not defined" ] } ], "source": [ "cassmates[0]='Tom'" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "这里**classmates**这个$tuple$不能变了，它也没有**append()，insert()**这样的方法。
\n", "其他获取元素的方法和list是一样的，你可以正常地使用**classmates[0]，classmates[-1]**，但不能赋值成另外的元素。
\n", "**不可变的tuple有什么意义？**:因为tuple不可变，所以代码更安全。如果可能，能用tuple代替list就尽量用tuple。" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "tuple的陷阱：**当你定义一个tuple时，在定义的时候，tuple的元素就必须被确定下来，比如：**" ] }, { "cell_type": "code", "execution_count": 53, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "(1, 2)" ] }, "execution_count": 53, "metadata": {}, "output_type": "execute_result" } ], "source": [ "t = (1, 2)\n", "t" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "定义一个空的tuple，可以写成()：" ] }, { "cell_type": "code", "execution_count": 54, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "()" ] }, "execution_count": 54, "metadata": {}, "output_type": "execute_result" } ], "source": [ "t = ()\n", "t" ] }, { "cell_type": "markdown", "metadata": {}, "source": [] }, { "cell_type": "code", "execution_count": 55, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "(1, int)" ] }, "execution_count": 55, "metadata": {}, "output_type": "execute_result" } ], "source": [ "# 定义的不是tuple，er而是1这个数！ 这是因为括号()既可以表示tuple，又可以表示数学公式中的小括号，这就产生了歧义\n", "t = (1)\n", "t,type(t)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "因此，Python规定，这种情况下，按小括号进行计算，计算结果自然是1。\n", "所以，只有1个元素的tuple定义时必须加一个逗号,，来消除歧义：" ] }, { "cell_type": "code", "execution_count": 56, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "((1,), tuple)" ] }, "execution_count": 56, "metadata": {}, "output_type": "execute_result" } ], "source": [ "# 所以，只有1个元素的tuple定义时必须加一个逗号,，来消除歧义：\n", "t = (1,)\n", "t,type(t)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**“可变的”tuple：**" ] }, { "cell_type": "code", "execution_count": 57, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "('a', 'b', ['X', 'Y'])" ] }, "execution_count": 57, "metadata": {}, "output_type": "execute_result" } ], "source": [ "t = ('a', 'b', ['A', 'B'])\n", "t[2][0] = 'X'\n", "t[2][1] = 'Y'\n", "t" ] }, { "cell_type": "code", "execution_count": 58, "metadata": {}, "outputs": [ { "ename": "TypeError", "evalue": "'tuple' object does not support item assignment", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mt\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m2\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m=\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;36m2\u001b[0m\u001b[1;33m]\u001b[0m \u001b[1;31m#\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mTypeError\u001b[0m: 'tuple' object does not support item assignment" ] } ], "source": [ "t[2]=[1,2] #" ] }, { "cell_type": "code", "execution_count": 60, "metadata": {}, "outputs": [], "source": [ "# t[0]='aa' #tuple是不可变的，改变t[0]会出错" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**原始的内存结构：**
\n", "![alt text](002List-Tuple2.png)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**把list的元素'A'和'B'修改为'X'和'Y'后：**
\n", "![alt text](002List-Tuple2.png)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "表面上看，tuple的元素确实变了，但其实变的不是tuple的元素，而是list的元素。
\n", "tuple一开始指向的list并没有改成别的list，所以，tuple所谓的“不变”是说**tuple的每个元素，指向永远不变。**即指向'a'，就不能改成指向'b'，指向一个list，就不能改成指向其他对象，**但指向的这个list本身是可变的！**\n", "\n", "要创建一个内容也不变的tuple怎么做？那就必须保证tuple的每一个元素本身也不能变。" ] }, { "cell_type": "code", "execution_count": null, "metadata": {}, "outputs": [], "source": [] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# 列表与元组的速度比较\n", "IPython 中用 magic 命令 %timeit 来计时。" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 比较生成速度\n", "元组的生成速度要比列表的生成速度快得多，相差大概一个数量级。" ] }, { "cell_type": "code", "execution_count": 59, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "149 ns ± 7.18 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)\n" ] } ], "source": [ "%timeit [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": 60, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "9.28 ns ± 0.72 ns per loop (mean ± std. dev. of 7 runs, 100000000 loops each)\n" ] } ], "source": [ "%timeit (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", "metadata": {}, "source": [ "## 比较遍历速度\n", "产生内容相同的随机列表和元组：\n", "在遍历上，元组和列表的速度表现差不多。" ] }, { "cell_type": "code", "execution_count": 61, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "10000" ] }, "execution_count": 61, "metadata": {}, "output_type": "execute_result" } ], "source": [ "from numpy.random import rand\n", "values = rand(10000,4)\n", "lst = [list(row) for row in values]\n", "tup = tuple(tuple(row) for row in values)\n", "len(values)" ] }, { "cell_type": "code", "execution_count": 62, "metadata": {}, "outputs": [ { "data": { "text/plain": [ "array([[0.14684551, 0.60337232, 0.70082914, 0.36526826],\n", " [0.4619078 , 0.8830263 , 0.71600454, 0.7315442 ]])" ] }, "execution_count": 62, "metadata": {}, "output_type": "execute_result" } ], "source": [ "values[0:2]" ] }, { "cell_type": "code", "execution_count": 63, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "1.2 ms ± 75.3 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)\n" ] } ], "source": [ " %timeit for row in lst: list(row)" ] }, { "cell_type": "code", "execution_count": 64, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "742 µs ± 65.3 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)\n" ] } ], "source": [ "%timeit for row in tup: tuple(row)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 比较遍历和索引速度：\n", "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。" ] }, { "cell_type": "code", "execution_count": 65, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "2.8 ms ± 104 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)\n" ] } ], "source": [ "%timeit for row in lst: a = row[0] + 1" ] }, { "cell_type": "code", "execution_count": 66, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "3.25 ms ± 142 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": "code", "execution_count": null, "metadata": {}, "outputs": [], "source": [] }, { "cell_type": "code", "execution_count": null, "metadata": {}, "outputs": [], "source": [] }, { "cell_type": "code", "execution_count": null, "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": "3.8.20" }, "toc": { "base_numbering": 1, "nav_menu": {}, "number_sections": false, "sideBar": true, "skip_h1_title": false, "title_cell": "Table of Contents", "title_sidebar": "Contents", "toc_cell": false, "toc_position": {}, "toc_section_display": true, "toc_window_display": true } }, "nbformat": 4, "nbformat_minor": 4 }