02-python-essentials/02.10-dictionaries.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 字典 "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "字典 `dictionary` ，在一些编程语言中也称为 `hash` ， `map` ，是一种由键值对组成的数据结构。\n",
    "\n",
    "顾名思义，我们把键想象成字典中的单词，值想象成词对应的定义，那么——\n",
    "\n",
    "一个词可以对应一个或者多个定义，但是这些定义只能通过这个词来进行查询。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 基本操作"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 空字典"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**Python** 使用 `{}` 或者 `dict()` 来创建一个空的字典："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "dict"
      ]
     },
     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = {}\n",
    "type(a)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "dict"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = dict()\n",
    "type(a)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "有了dict之后，可以用索引键值的方法向其中添加元素，也可以通过索引来查看元素的值："
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 插入键值"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'one': 'this is number 1', 'two': 'this is number 2'}"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a[\"one\"] = \"this is number 1\"\n",
    "a[\"two\"] = \"this is number 2\"\n",
    "a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 查看键值"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'this is number 1'"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a['one']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 更新键值"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'one': 'this is number 1, too', 'two': 'this is number 2'}"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a[\"one\"] = \"this is number 1, too\"\n",
    "a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 初始化字典"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "可以看到，Python使用`key: value`这样的结构来表示字典中的元素结构，事实上，可以直接使用这样的结构来初始化一个字典："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'this is number 1'"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "b = {'one': 'this is number 1', 'two': 'this is number 2'}\n",
    "b['one']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 字典没有顺序"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "当我们 `print` 一个字典时，**Python**并不一定按照插入键值的先后顺序进行显示,因为字典中的键本身不一定是有序的。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'two': 'this is number 2', 'one': 'this is number 1, too'}\n"
     ]
    }
   ],
   "source": [
    "print a"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'two': 'this is number 2', 'one': 'this is number 1'}\n"
     ]
    }
   ],
   "source": [
    "print b"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "因此，**Python**中不能用支持用数字索引按顺序查看字典中的值，而且数字本身也有可能成为键值，这样会引起混淆："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "0",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-9-cc39af2a359c>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# 会报错\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[0ma\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mKeyError\u001b[0m: 0"
     ]
    }
   ],
   "source": [
    "# 会报错\n",
    "a[0]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 键必须是不可变的类型"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "出于hash的目的，Python中要求这些键值对的**键**必须是**不可变**的，而值可以是任意的Python对象。\n",
    "\n",
    "一个表示近义词的字典："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'immutable': ['fixed',\n",
       "  'set',\n",
       "  'rigid',\n",
       "  'inflexible',\n",
       "  'permanent',\n",
       "  'established',\n",
       "  'carved in stone'],\n",
       " 'mutable': ['changeable',\n",
       "  'variable',\n",
       "  'varying',\n",
       "  'fluctuating',\n",
       "  'shifting',\n",
       "  'inconsistent',\n",
       "  'unpredictable',\n",
       "  'inconstant',\n",
       "  'fickle',\n",
       "  'uneven',\n",
       "  'unstable',\n",
       "  'protean']}"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "synonyms = {}\n",
    "synonyms['mutable'] = ['changeable', 'variable', 'varying', 'fluctuating',\n",
    "                       'shifting', 'inconsistent', 'unpredictable', 'inconstant',\n",
    "                       'fickle', 'uneven', 'unstable', 'protean']\n",
    "synonyms['immutable'] = ['fixed', 'set', 'rigid', 'inflexible', \n",
    "                         'permanent', 'established', 'carved in stone']\n",
    "synonyms"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "另一个例子："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{500: {'mag': 0.05, 'width': 20},\n",
       " 760: {'mag': 0.04, 'width': 25},\n",
       " 3001: {'mag': 0.05, 'width': 80},\n",
       " 4180: {'mag': 0.03, 'width': 30}}"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# 定义四个字典\n",
    "e1 = {'mag': 0.05, 'width': 20}\n",
    "e2 = {'mag': 0.04, 'width': 25}\n",
    "e3 = {'mag': 0.05, 'width': 80}\n",
    "e4 = {'mag': 0.03, 'width': 30}\n",
    "# 以字典作为值传入新的字典\n",
    "events = {500: e1, 760: e2, 3001: e3, 4180: e4}\n",
    "events"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "键（或者值）的数据类型可以不同："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[{'first': 'Sam', 'last': 'Malone', 'name': 35},\n",
       " {'first': 'Woody', 'last': 'Boyd', 'name': 21},\n",
       " {'first': 'Norm', 'last': 'Peterson', 'name': 34},\n",
       " {'first': 'Diane', 'last': 'Chambers', 'name': 33}]"
      ]
     },
     "execution_count": 13,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "people = [\n",
    "    {'first': 'Sam', 'last': 'Malone', 'name': 35},\n",
    "    {'first': 'Woody', 'last': 'Boyd', 'name': 21},\n",
    "    {'first': 'Norm', 'last': 'Peterson', 'name': 34},\n",
    "    {'first': 'Diane', 'last': 'Chambers', 'name': 33}\n",
    "]\n",
    "people"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 使用 dict 初始化字典"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "除了通常的定义方式，还可以通过 `dict()` 转化来生成字典："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'foozelator': 123, 'frombicator': 18, 'snitzelhogen': 23, 'spatzleblock': 34}"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "inventory = dict(\n",
    "    [('foozelator', 123),\n",
    "     ('frombicator', 18), \n",
    "     ('spatzleblock', 34), \n",
    "     ('snitzelhogen', 23)\n",
    "    ])\n",
    "inventory"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "利用索引直接更新键值对："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'foozelator': 123, 'frombicator': 19, 'snitzelhogen': 23, 'spatzleblock': 34}"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "inventory['frombicator'] += 1\n",
    "inventory"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 适合做键的类型"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "在不可变类型中，整数和字符串是字典中最常用的类型；而浮点数通常不推荐用来做键，原因如下："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "3.3",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-16-a48e87d01daa>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[0mdata\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m1.1\u001b[0m \u001b[1;33m+\u001b[0m \u001b[1;36m2.2\u001b[0m\u001b[1;33m]\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;36m6.6\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      3\u001b[0m \u001b[1;31m# 会报错\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 4\u001b[1;33m \u001b[0mdata\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m3.3\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mKeyError\u001b[0m: 3.3"
     ]
    }
   ],
   "source": [
    "data = {}\n",
    "data[1.1 + 2.2] = 6.6\n",
    "# 会报错\n",
    "data[3.3]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "事实上，观察`data`的值就会发现，这个错误是由浮点数的精度问题所引起的："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{3.3000000000000003: 6.6}"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "data"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "有时候，也可以使用元组作为键值，例如，可以用元组做键来表示从第一个城市飞往第二个城市航班数的多少："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "connections = {}\n",
    "connections[('New York', 'Seattle')] = 100\n",
    "connections[('Austin', 'New York')] = 200\n",
    "connections[('New York', 'Austin')] = 400"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "元组是有序的，因此 `('New York', 'Austin')` 和 `('Austin', 'New York')` 是两个不同的键："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "200\n",
      "400\n"
     ]
    }
   ],
   "source": [
    "print connections[('Austin', 'New York')]\n",
    "print connections[('New York', 'Austin')]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 字典方法"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "###  `get` 方法"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "之前已经见过，用索引可以找到一个键对应的值，但是当字典中没有这个键的时候，Python会报错，这时候可以使用字典的 `get` 方法来处理这种情况，其用法如下：\n",
    "\n",
    "    `d.get(key, default = None)`\n",
    "\n",
    "返回字典中键 `key` 对应的值，如果没有这个键，返回 `default` 指定的值（默认是 `None` ）。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "a = {}\n",
    "a[\"one\"] = \"this is number 1\"\n",
    "a[\"two\"] = \"this is number 2\""
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "索引不存在的键值会报错："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "ename": "KeyError",
     "evalue": "'three'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mKeyError\u001b[0m                                  Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-22-8a5f2913f00e>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0ma\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;34m\"three\"\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mKeyError\u001b[0m: 'three'"
     ]
    }
   ],
   "source": [
    "a[\"three\"]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "改用get方法："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "None\n"
     ]
    }
   ],
   "source": [
    "print a.get(\"three\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "指定默认值参数："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'undefined'"
      ]
     },
     "execution_count": 25,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a.get(\"three\", \"undefined\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### `pop` 方法删除元素"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`pop` 方法可以用来弹出字典中某个键对应的值，同时也可以指定默认参数：\n",
    "\n",
    "    `d.pop(key, default = None)`\n",
    "\n",
    "删除并返回字典中键 `key` 对应的值，如果没有这个键，返回 `default` 指定的值（默认是 `None` ）。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'one': 'this is number 1', 'two': 'this is number 2'}"
      ]
     },
     "execution_count": 26,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "弹出并返回值："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "metadata": {
    "collapsed": false,
    "scrolled": true
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'this is number 2'"
      ]
     },
     "execution_count": 27,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a.pop(\"two\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{'one': 'this is number 1'}"
      ]
     },
     "execution_count": 28,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "弹出不存在的键值："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'not exist'"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a.pop(\"two\", 'not exist')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "与列表一样，`del` 函数可以用来删除字典中特定的键值对，例如："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "{}"
      ]
     },
     "execution_count": 30,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "del a[\"one\"]\n",
    "a"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### `update`方法更新字典"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "之前已经知道，可以通过索引来插入、修改单个键值对，但是如果想对多个键值对进行操作，这种方法就显得比较麻烦，好在有 `update` 方法：\n",
    "\n",
    "    `d.update(newd)`\n",
    "\n",
    "将字典`newd`中的内容更新到`d`中去。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'born': 1831, 'last': 'Maxwell', 'first': 'Jmes'}\n"
     ]
    }
   ],
   "source": [
    "person = {}\n",
    "person['first'] = \"Jmes\"\n",
    "person['last'] = \"Maxwell\"\n",
    "person['born'] = 1831\n",
    "print person"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "把'first'改成'James'，同时插入'middle'的值'Clerk'："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "{'middle': 'Clerk', 'born': 1831, 'last': 'Maxwell', 'first': 'James'}\n"
     ]
    }
   ],
   "source": [
    "person_modifications = {'first': 'James', 'middle': 'Clerk'}\n",
    "person.update(person_modifications)\n",
    "print person"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### `in`查询字典中是否有该键"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "barn = {'cows': 1, 'dogs': 5, 'cats': 3}"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`in` 可以用来判断字典中是否有某个特定的键："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 35,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 35,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "'chickens' in barn"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 34,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "'cows' in barn"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### `keys` 方法，`values` 方法和`items` 方法"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "    `d.keys()` \n",
    "\n",
    "返回一个由所有键组成的列表；\n",
    "\n",
    "    `d.values()` \n",
    "\n",
    "返回一个由所有值组成的列表；\n",
    "\n",
    "    `d.items()` \n",
    "\n",
    "返回一个由所有键值对元组组成的列表；"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['cows', 'cats', 'dogs']"
      ]
     },
     "execution_count": 36,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "barn.keys()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[1, 3, 5]"
      ]
     },
     "execution_count": 37,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "barn.values()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 38,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "[('cows', 1), ('cats', 3), ('dogs', 5)]"
      ]
     },
     "execution_count": 38,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "barn.items()"
   ]
  }
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