3.7字典

字典dictionary
字段是python中唯一的映射关系。采用键值对（key-value）存储数据。Python对key进行哈希函数运算，根据计算结果决定value的存储位置，所以字典是无序列的，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。

# -*-coding:utf-8 -*-
__date__ = '2018/2/7 9:50'
__author__ = 'xiaojiaxin'
__file_name__ = 'dict1'

#创建字典方法1
dict1={1:[1,2,3],2:"1000","name":"jiaxin"}
print(dict1)
print(dict1[1])
print(dict1["name"])

a=list((1,2,3))   #创建列表的新方法
print(a)
a=list([1,2,3])    #只需要在list()放一个序列，就可以转换成一个列表
print(a)
a=list("123")
print(a)
#创建字典方法2，不常用
dict2=dict(((1,"a"),(2,'b'),(3,'c'),))   #里面放键值对
print(dict2)

#增删改查

#增加
dict2["age"]=50
print(dict2)
#键存在不改值，不存在就创建键和值
return1=dict2.setdefault("home","ZHEJIANG")   #setdefault有返回值
print(dict2)
print(return1)
dict2.setdefault("hobby")
print(dict2)

#查
print(dict2["hobby"])
print(dict2[1])
print(dict2.keys())  #查找字段的所有键
#dict_keys([1, 2, 3, 'age', 'home', 'hobby'])  #不是列表类型，是dict_keys新的数据类型
print(list(dict2.keys()))    #转换成list类型使用
print(dict2.values())
print(dict2.items())

#改
dict2["name"]="jiaxin1"
print(dict2)

dict3={"name":"jiaxin3",10:"10"}
dict2.update(dict3)   #原值会被新值覆盖掉
print(dict3)
print(dict2)

#删
del dict3["name"]
print(dict3)
print(dict3.clear())
del dict3
ruturn2=dict2.pop(10)
print(dict2)
print(ruturn2)
return3=dict2.popitem()    #随机删除一组键值对，意义不大
print(dict2)
print(return3)

{1: [1, 2, 3], 2: '1000', 'name': 'jiaxin'}
[1, 2, 3]
jiaxin
[1, 2, 3]
[1, 2, 3]
['1', '2', '3']
{1: 'a', 2: 'b', 3: 'c'}
{1: 'a', 2: 'b', 3: 'c', 'age': 50}
{1: 'a', 2: 'b', 3: 'c', 'age': 50, 'home': 'ZHEJIANG'}
ZHEJIANG
{1: 'a', 2: 'b', 3: 'c', 'age': 50, 'home': 'ZHEJIANG', 'hobby': None}
None
a
dict_keys([1, 2, 3, 'age', 'home', 'hobby'])
[1, 2, 3, 'age', 'home', 'hobby']
dict_values(['a', 'b', 'c', 50, 'ZHEJIANG', None])
dict_items([(1, 'a'), (2, 'b'), (3, 'c'), ('age', 50), ('home', 'ZHEJIANG'), ('hobby', None)])
{1: 'a', 2: 'b', 3: 'c', 'age': 50, 'home': 'ZHEJIANG', 'hobby': None, 'name': 'jiaxin1'}
{'name': 'jiaxin3', 10: '10'}
{1: 'a', 2: 'b', 3: 'c', 'age': 50, 'home': 'ZHEJIANG', 'hobby': None, 'name': 'jiaxin3', 10: '10'}
{10: '10'}
None
{1: 'a', 2: 'b', 3: 'c', 'age': 50, 'home': 'ZHEJIANG', 'hobby': None, 'name': 'jiaxin3'}
10
{1: 'a', 2: 'b', 3: 'c', 'age': 50, 'home': 'ZHEJIANG', 'hobby': None, 'name': 'jiaxin3'}

其他操作及方法
#其他操作及方法

#深浅拷贝学完再看
dict4=dict2.fromkeys(["host1","host2","host3"],"test")
print(dict4)

dict5=dict2.fromkeys(["host1","host2","host3"],["test","test2"])
print(dict5)
dict5["host2"][1]='test3'    #实际效果是全部都改了
print(dict5)

{'host1': 'test', 'host2': 'test', 'host3': 'test'}
{'host1': ['test', 'test2'], 'host2': ['test', 'test2'], 'host3': ['test', 'test2']}
{'host1': ['test', 'test3'], 'host2': ['test', 'test3'], 'host3': ['test', 'test3']}

#排序

dict6={1:"111",2:"222",3:"13"}
print(sorted(dict6))   #只对键进行排序,只输出键
print(sorted(dict6.items()))     #对键进行排序，输出键值对

[1, 2, 3]
[(1, '111'), (2, '222'), (3, '13')]

#遍历 很重要！！！！！

print(dict2)
for i in dict2:
    print(i)

# 1
# 2
# 3
# age
# home
# hobby

for m,n in enumerate(dict2):
    print(m,"---",n)
# 0 --- 1
# 1 --- 2
# 2 --- 3
# 3 --- age
# 4 --- home
# 5 --- hobby
for m1,n1 in dict2.items():   #效率不高
    print(m1,">>>",n1)
# 1 >>> a
# 2 >>> b
# 3 >>> c
# age >>> 50
# home >>> ZHEJIANG
# hobby >>> None

for i in dict2:
    print(i,dict2[i])
# 1 a
# 2 b
# 3 c
# age 50
# home ZHEJIANG
# hobby None