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Commit 9905883

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Relph1119Relph1119
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🎉 学习第6章对象引用、可变性和垃圾回收
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‎notes/ch06.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"id": "65065ec2",
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"metadata": {},
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"source": [
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"# 第6章 对象引用、可变性和垃圾回收"
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]
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},
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{
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"cell_type": "markdown",
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"id": "5b56a0e0",
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"metadata": {},
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"source": [
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"## 6.1 浅拷贝"
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]
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},
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{
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"cell_type": "markdown",
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"id": "5bd3b687",
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"metadata": {},
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"source": [
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"浅拷贝的方式：\n",
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"\n",
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"- 复制列表使用内置的类型构造函数。\n",
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"- 使用`[:]`进行浅拷贝。\n",
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"- 使用`copy.copy`函数进行浅拷贝。"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"id": "28724977",
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"l1: [3, [66, 44], (7, 8, 9), 100]\n",
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"l2: [3, [66, 44], (7, 8, 9)]\n",
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"l1: [3, [66, 44, 33, 22], (7, 8, 9), 100]\n",
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"l2: [3, [66, 44, 33, 22], (7, 8, 9, 10, 11)]\n"
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]
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}
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],
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"source": [
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"l1 = [3, [66, 55, 44], (7, 8, 9)]\n",
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"l2 = list(l1)\n",
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"l1.append(100)\n",
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"l1[1].remove(55)\n",
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"print('l1:', l1)\n",
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"print('l2:', l2)\n",
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"l2[1] += [33, 22]\n",
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"l2[2] += (10, 11)\n",
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"print('l1:', l1)\n",
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"print('l2:', l2)"
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]
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},
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{
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"cell_type": "markdown",
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"id": "ebfc3e0f",
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"metadata": {},
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"source": [
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"![浅拷贝可视化](./images/06-01-python-vis.png)"
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]
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},
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{
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"cell_type": "markdown",
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"id": "3aa648d4",
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"metadata": {},
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"source": [
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"深拷贝方式：使用`copy.deepcopy`函数"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"id": "ab619f2d",
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"metadata": {},
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"outputs": [],
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"source": [
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"# 校车乘客在途中有上有下\n",
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"class Bus:\n",
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" def __init__(self, passengers=None):\n",
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" if passengers is None:\n",
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" self.passengers = []\n",
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" else:\n",
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" self.passengers = list(passengers)\n",
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"\n",
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" def pick(self, name):\n",
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" self.passengers.append(name)\n",
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"\n",
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" def drop(self, name):\n",
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" self.passengers.remove(name)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 6,
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"id": "64c4950f",
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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"['Alice', 'Claire', 'David']"
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]
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},
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"execution_count": 6,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"import copy\n",
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"bus1 = Bus(['Alice', 'Bill', 'Claire', 'David'])\n",
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"# 使用浅拷贝\n",
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"bus2 = copy.copy(bus1)\n",
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"# 使用深拷贝\n",
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"bus3 = copy.deepcopy(bus1)\n",
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"bus1.drop('Bill')\n",
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"bus2.passengers"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 7,
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"id": "3a0d3fdb",
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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"['Alice', 'Bill', 'Claire', 'David']"
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]
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},
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"execution_count": 7,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"bus3.passengers"
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]
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},
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{
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"cell_type": "markdown",
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"id": "6a67e690",
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"metadata": {},
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"source": [
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"## 6.2 防御可变参数"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 8,
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"id": "aa4c09bf",
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"metadata": {},
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"outputs": [],
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"source": [
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"class TwilightBus:\n",
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" \"\"\"让乘客销声匿迹的校车\"\"\"\n",
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"\n",
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" def __init__(self, passengers=None):\n",
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" if passengers is None:\n",
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" self.passengers = [] \n",
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" else:\n",
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" # WARN：不能直接引用变量，应使用浅拷贝\n",
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" self.passengers = passengers\n",
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"\n",
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" def pick(self, name):\n",
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" self.passengers.append(name)\n",
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"\n",
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" def drop(self, name):\n",
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" self.passengers.remove(name)"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 10,
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"id": "2d3fad06",
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"metadata": {},
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"outputs": [
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{
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"data": {
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"text/plain": [
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"['Sue', 'Maya', 'Diana']"
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]
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},
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"execution_count": 10,
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"metadata": {},
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"output_type": "execute_result"
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}
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],
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"source": [
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"basketball_team = ['Sue', 'Tina', 'Maya', 'Diana', 'Pat']\n",
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"bus = TwilightBus(basketball_team)\n",
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"bus.drop('Tina')\n",
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"bus.drop('Pat')\n",
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"# 下车的学生从篮球队中消失了！\n",
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"basketball_team"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 11,
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"id": "ee88a198",
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"metadata": {},
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"outputs": [],
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"source": [
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"# 修改后的代码\n",
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"class TwilightBus:\n",
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" \"\"\"让乘客销声匿迹的校车\"\"\"\n",
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"\n",
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" def __init__(self, passengers=None):\n",
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" if passengers is None:\n",
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" self.passengers = [] \n",
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" else:\n",
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" # 使用构造器的浅拷贝方式\n",
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" self.passengers = list(passengers)\n",
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"\n",
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" def pick(self, name):\n",
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" self.passengers.append(name)\n",
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"\n",
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" def drop(self, name):\n",
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" self.passengers.remove(name)"
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]
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},
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{
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"cell_type": "markdown",
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"id": "f92a2772",
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"metadata": {},
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"source": [
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"## 6.3 本章小结"
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]
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},
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{
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"cell_type": "markdown",
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"id": "ab233bbe",
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"metadata": {},
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"source": [
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"- 简单的赋值不创建副本，而是建立引用。\n",
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"- 对`+=`或`*=`增量赋值，如果左边的变量绑定的是不可变对象，则创建新对象，如果是可变对象，就地修改。\n",
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"- 为现有的变量赋予新值，不修改之前绑定的变量。如果变量是之前那个对象的最后一个引用，重新绑定了其他对象，则对象被当作垃圾回收。\n",
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"- 函数的形参以别名的形式传递，这意味着函数可能会修改通过实参传入的可变对象。\n",
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"- 使用可变类型作为函数参数的默认值，是危险的。如果修改了参数，默认值也会发生变化。"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3 (ipykernel)",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.10.5"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 5
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}

‎notes/images/06-01-python-vis.png

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