目录
Python字典
一、字典理解
1.1）创建字典与访问
1.2）字典长度
1.3）数据类型
二、访问字典
2.1）访问键名
2.2）访问健值
三、更改字典各种方法
四、添加字典项各种方法
五、删除字典的各种方法
六、遍历字典
七、复制字典
八、嵌套字典
九、练习
Python字典
一、字典理解
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。）
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": "China","model": "zhangsan","year": 1688
}
print(thisdict)
输出：
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": "China","model": "zhangsan","year": 1688，
}
print(thisdict["brand"])
输出：
字典不能有两个具有相同键的项目：重复值将覆盖现有值
thisdict = {"brand": "China","model": "zhangsan","year": 1688,"year": 2021
}
print(thisdict)
返回：
1.2）字典长度
还是用用len函数
thisdict = {"brand": "China","model": "zhangsan","year": 1688,
}
print(len(thisdict))输出：
1.3）数据类型
字典项中的值可以是任何数据类型：
例如：
thisdict = {"brand": "China","electric": False,"year": 1688,"colors": ["red", "white", "blue"]
}
类型：dict()
打印字典的数据类型：
thisdict = {"brand": "China","electric": False,"year": 1688,"colors": ["red", "white", "blue"]
}print(type(thisdict))
返回：
补充巩固：
二、访问字典
2.1）访问键名
您可以通过引用方括号内的键名来访问字典的项目：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
x = thisdict["name"]
print(x)
返回：
还有一个被调用的方法get()会给你同样的结果：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
x = thisdict["name"]
y=thisdict.get('name')
print(x)
print(y)
返回：
2.2）访问健值
keys()方法将返回字典中所有键的列表。
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
x = thisdict.keys()
print(x)
返回：
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": "笨小孩","address": "河北","year": 2000
}
thisdict['age']=20
print(thisdict)
返回：
获取值
values()方法将返回字典中所有值的列表。
x = thisdict.values()
items()方法将返回字典中的每个项目，作为列表中的元组。
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
thisdict['age']=20
print(thisdict)
x = thisdict.items()
print(x)
返回元祖：
要确定字典中是否存在指定的键，请使用in关键字：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
if 'name' in thisdict:print('name在字典')
返回：
三、更改字典各种方法
前面我们讲到了一部分更改内容，这里我们具体讲一下。
例如我要把川川改为川川菜鸟：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
thisdict['name'] = '笨洋洋'
print(thisdict)
返回：
或者我们使用update()方法：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
thisdict.update({'name':'笨洋洋'})
print(thisdict)
效果一样：
四、添加字典项各种方法
比如我要添加一个年龄为20：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
thisdict['age']=20
print(thisdict)
返回：
或者还是使用update:
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
thisdict['age']=20
print(thisdict)
thisdict.update({'age':'20岁'})
print(thisdict)
返回：
五、删除字典的各种方法
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": "笨小孩","address": "河北","year": 2000
}
thisdict.pop("address")
print(thisdict)
返回：
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": "笨小孩","address": "河北","year": 2000
}
thisdict.pop("address")
print(thisdict)
thisdict.popitem()
print(thisdict)
返回：
del关键字删除与指定键名称的项目：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
del thisdict['name']
print(thisdict)
返回：
del关键字也可以删除字典完全：
del thisdict
clear()方法清空字典：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
thisdict.clear()
print(thisdict)
返回空：
六、遍历字典
将字典中的所有键名，一一打印出来：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
for x in thisdict:print(x)
输出：
一一打印字典中的所有值：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
for x in thisdict:print(thisdict[x])返回：
您还可以使用该values()方法返回字典的值：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
for x in thisdict.values():print(x)
输出：
您可以使用该keys()方法返回字典的键：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
for x in thisdict.keys():print(x)
返回：
使用以下 方法循环遍历keys和valuesitems()：
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
for x, y in thisdict.items():print(x, y)
返回：
七、复制字典
用copy()函数
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
mydict=thisdict.copy()
print(mydict)
输出：
内置dict(）函数
thisdict = {"name": "笨小孩","address": "河北","year": 2000
}
mydict=dict(thisdict)
print(mydict)
效果都一样：
八、嵌套字典
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)
返回：
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)
效果一样：
九、练习
1-使用get方法打印汽车字典的“model”键的值。
car = {"brand": "Ford","model": "Mustang","year": 1964
}
print
2-将“year”值从 1964 更改为 2020。
car = {"brand": "Ford","model": "Mustang","year": 1964
}3-将键/值对 “color” : “red” 添加到汽车字典中。
car = {"brand": "Ford","model": "Mustang","year": 1964
}4-使用 pop 方法从汽车字典中删除“model”。
car = {"brand": "Ford","model": "Mustang","year": 1964
}5-使用clear方法清空car字典。
car = {"brand": "Ford","model": "Mustang","year": 1964
}
