DAY 08冲击蓝桥杯——Python基础08python字典

9.1 字典的基本概念

基本形式：

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

字典用于在键值对中存储数据值。字典是有序*、可变且不允许重复的集合。（从 Python 3.7 版开始，字典是有序的。在 Python 3.6 及更早版本中，字典是无序的。）

9.1.1 创建字典与访问

字典是用大括号写的，有键和值。
创建并打印字典：

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}

字典项是有序的、可变的，并且不允许重复。字典项以键值对的形式呈现，可以使用键名进行引用。
例如打印brand的值

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict["brand"])

9.1.2 字典长度

还是用用len函数

hisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964,
  "year": 2020
}
print(len(thisdict))

9.1.3 数据类型

(1)字典项中的值可以是任何数据类型：
例如：

thisdict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}

类型：dict()
(2)打印字典的数据类型：

thisdict = {
  "brand": "Ford",
  "electric": False,
  "year": 1964,
  "colors": ["red", "white", "blue"]
}
print(type(thisdict))

(3)与其他数据类型的区别
列表是有序且可变的，允许重复元素；
元组是有序且不可更改的，允许重复元素；
集合是无序且无索引的，无重复元素；
字典是有序且可变的，无重复元素。

9.2 字典的“增”

9.2.1 关键词索引添加

比如我要添加一个年龄为20：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict['age']=21
print(thisdict)

9.2.2 使用update

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict['age']=21
print(thisdict)
thisdict.update({'age':'21岁'})
print(thisdict)

9.3 字典的“删”

9.3.1 pop()方法

删除具有指定键名的项。
比如我要删除地址项目：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
print(thisdict)
thisdict.pop("address")
print(thisdict)

9.3.2 popitem()方法

删除最后插入的项目（在 3.7 之前的版本中，将删除随机项目）：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict.pop("address")
print(thisdict)
thisdict.popitem()
print(thisdict)

9.3.3 del关键字

删除与指定键名称的项目：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
del thisdict['name']
print(thisdict)

也可以完全删除该字典。

9.3.4 clear()方法

清空字典：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict.clear()
print(thisdict)

9.4 字典的“改”

9.4.1 关键词索引

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict['name'] = 'hg菜鸟'
print(thisdict)

9.4.2 使用update()方法：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict.update({'name':'hg菜鸟'})
print(thisdict)

9.5 字典的“查”

9.5.1 访问键名

(1)可以通过引用方括号内的键名来访问字典的项目：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
x = thisdict["name"]
print(x)

(2)还有一个被调用的方法get()会给你同样的结果：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
x = thisdict["name"]
y=thisdict.get('name')
print(x)
print(y)

9.5.2 访问键值

（1）keys()方法将返回字典中所有键的列表。

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
x = thisdict.keys()
print(x)

（2）向原始字典添加一个新项目，并看到键列表也得到更新：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict['age']=20
print(thisdict)

（3）获取值

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
x = thisdict.values()
print(x)

（4）items()方法将返回字典中的每个项目，作为列表中的元组。

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
thisdict['age']=20
print(thisdict)
x = thisdict.items()
print(x)

（5）要确定字典中是否存在指定的键，请使用in关键字：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
if 'name' in thisdict:
    print('name在字典')

9.6 遍历字典

9.6.1 打印字典中的所有键名

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
for x in thisdict:
  print(x)

9.6.2 打印字典中的所有值：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
for x in thisdict:
  print(thisdict[x])

9.6.3 使用values()方法返回字典的值：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
for x in thisdict.values():
  print(x)

9.6.4 可以使用该keys()方法返回字典的键：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
for x in thisdict.keys():
  print(x)

9.6.5 使用以下方法循环遍历keys和valuesitems()：

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
for x, y in thisdict.items():
  print(x, y)

9.7 复制字典

9.7.1 用copy()函数

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
mydict=thisdict.copy()
print(mydict)

9.7.2 内置dict(）函数

thisdict = {
  "name": "hg",
  "address": "长沙",
  "year": 2000
}
mydict=dict(thisdict)
print(mydict)

9.8 字典的嵌套

创建一个包含三个字典的字典：

myfamily = {
  "child1" : {
    "name" : "Emil",
    "year" : 2004
  },
  "child2" : {
    "name" : "Tobias",
    "year" : 2007
  },
  "child3" : {
    "name" : "Linus",
    "year" : 2011
  }
}
print(myfamily)

创建三个字典，然后创建一个包含其他三个字典的字典：

child1 = {
  "name" : "Emil",
  "year" : 2004
}
child2 = {
  "name" : "Tobias",
  "year" : 2007
}
child3 = {
  "name" : "Linus",
  "year" : 2011
}

myfamily = {
  "child1" : child1,
  "child2" : child2,
  "child3" : child3
}
print(myfamily)

练习题

Q1-使用get方法打印汽车字典的“model”键的值。

car =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(car.get("model"))

Q2-将“year”值从 1964 更改为 2020。

car =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
car["year"]=2020
print(car)

Q3-将键/值对 “color” : “red” 添加到汽车字典中。

car =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
car["color"]="red"
print(car)

Q4-使用 pop 方法从汽车字典中删除“model”。

car =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
car.pop("model")
print(car)

Q5-使用clear方法清空car字典。

car =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
car.clear()
print(car)

answer都经过python调试。

1. https://chuanchuan.blog.csdn.net/article/details/120419754?spm=1001.2014.3001.5502

2. 用Python玩转数据——中国大学mooc