(十二)字典简介及字典的用法

第二步：找规律，有多少数据，就找2的多少次方，如果有42亿数据，找32次就找出来了。

----增
----删
----改
----查
names = {
    "stu1101":{"name":"Alex","age":22,"hobbie":"girl"},
    "stu1102":"Jack",
    "stu1103":"rain",
}
查：
（1）print(names["stu1101"]["hobbie"])-----------查
print(names["stu1104"]["hobbie"])-------------stu1104没有会报错-----------------------先判断在不在：
（2）print("stu1101" in names )----------------------True---在
print("stu1104" in names )----------------------False----不在
(3)print(names.get("stu1104"))----------没有返回一个 none
print(names.get("stu1101"))-------------有的话返回值
print(names.get("stu1104","asdfg"))------自定义一个值，返回asdfg
增：
names["stu1104"] = ["yangJian",31,"DBA"]
print(names)
改：
names["stu1104"][0] = "YANGJIAN"
print(names)
删：
(1)print(names.pop("stu1102"))
print(names)
(2)del names["stu1103"]
print(names)
————————————————————————————————————————————————
formkeys:
(1)
names = ["Jack","alex","eric"]
print (dict.fromkeys(names,0))
(2)
names = ["Jack","alex","eric"]
n3 = dict.fromkeys(names,1)
n3["Jack"]=2
print(n3)
{‘Jack‘: 2, ‘alex‘: 1, ‘eric‘: 1}
(3)
names = ["Jack","alex","eric"]
n3 = dict.fromkeys(names,[1,2,3])
n3["Jack"][1]=9
print(n3)
{‘Jack‘: [1, 9, 3], ‘alex‘: [1, 9, 3], ‘eric‘: [1, 9, 3]}-----为什么都变了?
看内存地址：
names = ["Jack","alex","eric"]
n3 = dict.fromkeys(names,[1,2,3])
#n3["Jack"][1]=9
print(id(n3["Jack"]),id(n3["eric"]))
5961568 5961568-----------------------------------------------内存地址一样
解释： a = 23 b =a a =40 b =23
a = [1,2,3]
b =a
现在把里面的2改成9，这时候a没有开辟新的内存空间
，只是把2变成9，内存空间不变化
————————————————————————————————————
items：一般来做循环
因为print(names.items())得到一个这样的列表： (‘stu1102‘, ‘Jack‘), (‘stu1103‘, ‘rain‘)
变成一个元组，有k，v
(1)for key in names:
    print(key,names[key])--------效率高

(2)for k,v in names.items():-----效率低
    print(k,v)
 -------------------------------------------------------------
keys  vlaus
print(names.keys())
print(names.values())
-----------------------------------------------------------
popitem------随机删除
names.popitem()
print(names)
----------------------------------------------------------
setdefault:
print(names.setdefault("stu1106","Racheal"))
print(names)
---------------------------------------------------------
update:合并2个字典
d1 ={"stu1102":"JACK",1:333,2:444}
names.update(d1)
print(names)
--------------------------------------------------------
字典的特性：无序，去重，查询效率高
--------------------------------------------------------
copy:
names = {
    "stu1101":{"name":"Alex","age":22,"hobbie":"girl"},
    "stu1102":"Jack",
    "stu1103":"rain",
}
n2 = names.copy()
print(names)
print(n2)
-----------------------------------------------------------
names = {
    "stu1101":{"name":"Alex","age":22,"hobbie":"girl"},
    "stu1102":"Jack",
    "stu1103":"rain",
}
n2 = names.copy()
names["stu1103"] = "RAIN"________________________________>>>
print(names)
print(n2)

{‘stu1101‘: {‘name‘: ‘Alex‘, ‘age‘: 22, ‘hobbie‘: ‘girl‘}, ‘stu1102‘: ‘Jack‘, ‘stu1103‘: ‘RAIN‘}
{‘stu1101‘: {‘name‘: ‘Alex‘, ‘age‘: 22, ‘hobbie‘: ‘girl‘}, ‘stu1102‘: ‘Jack‘, ‘stu1103‘: ‘rain‘}

-----------------------------------------------------------------------------------------------
names = {
    "stu1101":{"name":"Alex","age":22,"hobbie":"girl"},
    "stu1102":"Jack",
    "stu1103":"rain",
}
n2 = names.copy()
names["stu1103"] = "RAIN"
names["stu1101"]["age"]= 24-------------------------------->>
print(names)
print(n2)

{‘stu1101‘: {‘name‘: ‘Alex‘, ‘age‘: 24, ‘hobbie‘: ‘girl‘}, ‘stu1102‘: ‘Jack‘, ‘stu1103‘: ‘RAIN‘}
{‘stu1101‘: {‘name‘: ‘Alex‘, ‘age‘: 24, ‘hobbie‘: ‘girl‘}, ‘stu1102‘: ‘Jack‘, ‘stu1103‘: ‘rain‘}
----------------------------------------------------------------------------------------