字典是python中唯一的映射类型，采用键值对（key-value）的形式存储数据。python对key进行哈希函数运算，根据计算的结果决定value的存储地址，所以字典是无序存储的，且key必须是可哈希的。可哈希表示key必须是不可变类型，如：数字、字符串、元组。
字典(dictionary)是除列表意外python之中最灵活的内置数据结构类型。列表是有序的对象结合，字典是无序的对象集合。两者之间的区别在于：字典当中的元素是通过键来存取的，而不是通过偏移存取。
创建字典：
= {::}
shop2 = ((()))
()
(shop2)
输出：
{‘iphone‘: 2000, ‘book‘: ‘python‘}
{‘iphone7s‘: ‘new‘}
对应操作：
1、增
= {}
[] = [] = ()
shop1 = .setdefault()(shop1)
shop2 = .setdefault()(shop2)
()
输出：
{‘iphone7s‘: ‘new‘, ‘price‘: 8000}
8000
JD
{‘iphone7s‘: ‘new‘, ‘price‘: 8000, ‘buy‘: ‘JD‘}
2、查
= {: : : }
(.items())
(.keys())
(.values())
([])
(.get())
(.get())
()
((.values()))
输出：
dict_items([(‘iphone7s‘, ‘new‘), (‘price‘, 8000), (‘buy‘, ‘JD‘)])
dict_keys([‘iphone7s‘, ‘price‘, ‘buy‘])
dict_values([‘new‘, 8000, ‘JD‘])
JD
JD
False
True
[‘new‘, 8000, ‘JD‘]
3、改
= {: : : }
[] = shop1 = {::}
.update(shop1)
()
输出：
{‘iphone7s‘: ‘old‘, ‘price‘: 8000, ‘buy‘: ‘JD‘, ‘iphone5‘: ‘True‘, ‘size‘: 500}
4、删
shop = {‘iphone7s‘: ‘old‘, ‘price‘: 8000, ‘buy‘: ‘JD‘, ‘iphone5‘: ‘True‘, ‘size‘: 500}
del shop[‘size‘]#删除字典中指定键值对
print(shop)
shop1 = shop.pop(‘iphone5‘)#删除字典中指定键值对，并返回该键值对的值
print(shop1)
print(shop)
shop2 = shop.popitem()#随机删除某组键值对，并以元组方式返回值
print(shop2)
print(shop)
shop.clear()# 清空字典
print(shop)
输出：
{‘iphone7s‘: ‘old‘, ‘price‘: 8000, ‘buy‘: ‘JD‘, ‘iphone5‘: ‘True‘}
True
{‘iphone7s‘: ‘old‘, ‘price‘: 8000, ‘buy‘: ‘JD‘}
(‘buy‘, ‘JD‘)
{‘iphone7s‘: ‘old‘, ‘price‘: 8000}
{}
5、内置方法
dict.fromkeys
=.fromkeys([]) () []=() =.fromkeys([][]) () [][]=()
输出：
{‘host1‘: ‘test‘, ‘host2‘: ‘test‘, ‘host3‘: ‘test‘}
{‘host1‘: ‘test‘, ‘host2‘: ‘abc‘, ‘host3‘: ‘test‘}
{‘host1‘: [‘test1‘, ‘tets2‘], ‘host2‘: [‘test1‘, ‘tets2‘], ‘host3‘: [‘test1‘, ‘tets2‘]}
{‘host1‘: [‘test1‘, ‘test3‘], ‘host2‘: [‘test1‘, ‘test3‘], ‘host3‘: [‘test1‘, ‘test3‘]}
={:::}
()
((.items()))
输出：
True
[(2, ‘666‘), (4, ‘444‘), (5, ‘555‘)]
={: : }
i :
(i[i])
iv .items():
(iv)
item .items():
(item)
输出：
name joker
age 18
name joker
age 18
(‘name‘, ‘joker‘)
(‘age‘, 18)