python学习笔记字典

Posted 2020-10-04

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：     

shop = {‘iphone‘:2000,‘book‘:‘python‘}
shop2 = dict(((‘iphone7s‘,‘new‘),))
print(shop)
print(shop2)

输出：

{‘iphone‘: 2000, ‘book‘: ‘python‘}

{‘iphone7s‘: ‘new‘}

对应操作：

1、增

shop = {}
shop[‘iphone7s‘] = ‘new‘
shop[‘price‘] = 8000
print(shop)
shop1 = shop.setdefault(‘price‘,9000)#键存在，不改动，返回字典中相应的键对应的值
print(shop1)
shop2 = shop.setdefault(‘buy‘,‘JD‘)#键不存在，在字典中中增加新的键值对，并返回相应的值
print(shop2)
print(shop)

输出：

{‘iphone7s‘: ‘new‘, ‘price‘: 8000}

8000

JD

{‘iphone7s‘: ‘new‘, ‘price‘: 8000, ‘buy‘: ‘JD‘}

2、查

shop = {‘iphone7s‘: ‘new‘, ‘price‘: 8000, ‘buy‘: ‘JD‘}
print(shop.items())
print(shop.keys())
print(shop.values())
print(shop[‘buy‘])
print(shop.get(‘buy‘,False))
print(shop.get(‘buys‘,False))
print(‘buy‘ in shop)
print(list(shop.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

shop = {‘iphone7s‘: ‘new‘, ‘price‘: 8000, ‘buy‘: ‘JD‘}
shop[‘iphone7s‘] = ‘old‘
shop1 = {‘iphone5‘:‘True‘,‘size‘:500}
shop.update(shop1)
print(shop)

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

dic6=dict.fromkeys([‘host1‘,‘host2‘,‘host3‘],‘test‘)
print(dic6)

dic6[‘host2‘]=‘abc‘
print(dic6)

dic6=dict.fromkeys([‘host1‘,‘host2‘,‘host3‘],[‘test1‘,‘tets2‘])
print(dic6)

dic6[‘host2‘][1]=‘test3‘
print(dic6)

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‘]}

dic={5:‘555‘,2:‘666‘,4:‘444‘}
print(5 in dic)
print(sorted(dic.items()))

输出：

True

[(2, ‘666‘), (4, ‘444‘), (5, ‘555‘)]

dic5={‘name‘: ‘joker‘, ‘age‘: 18}
for i in dic5:
    print(i,dic5[i])
for i,v in dic5.items():
    print(i,v)
for item in dic5.items():
    print(item)

输出：

name joker

age 18

name joker

age 18

(‘name‘, ‘joker‘)

(‘age‘, 18)

本文出自 “on_the_road” 博客，请务必保留此出处http://cqtesting.blog.51cto.com/8685091/1958823