python学习-19 字典

字典dict

1.dic = {key:value,key:value}

字典有{ }括住，字典的value可以是任意值，字典的key的值不包括列表和字典

di = {"age":18,"name":"john","a":True,"b":[1,2,"movie"],"c":(1,2,"ff",)}
print(di)

运算结果：

{'age': 18, 'name': 'john', 'a': True, 'b': [1, 2, 'movie'], 'c': (1, 2, 'ff')}

Process finished with exit code 0

2.取值（只能通过索引的方式，不能用切片的方式。因为字典是无序的）

di = {"age":18,"name":"john","a":True,"b":[1,2,"movie"],"c":(1,2,"ff",)}
v = di["c"][0]
print(v)

运行结果：

1

Process finished with exit code 0

3.删除

di = {"age":18,"name":"john","a":True,"b":[1,2,"movie"],"c":(1,2,"ff",)}
del di["b"][2]
print(di)

运行结果：

{'age': 18, 'name': 'john', 'a': True, 'b': [1, 2], 'c': (1, 2, 'ff')}

Process finished with exit code 0

4.循环（只能用for循环，不能用while，因为字典是无序的）

di = {"age":18,"name":"john","a":True,"b":[1,2,"movie"],"c":(1,2,"ff",)}
for k,v in di.items():
 print(k,v)

运行结果：

age 18
name john
a True
b [1, 2, 'movie']
c (1, 2, 'ff')

Process finished with exit code 0

5.方法

-根据序列创建字典并指定统一的值

a= dict.fromkeys(["age",123,""],222)
print(a)

运行结果：

{'age': 222, 123: 222, '': 222}

Process finished with exit code 0

-根据key取值，如果没有key，则为none

dic = {"a":1,"b":3}
v = dic.get("a")
print(v)

运行结果：

1

Process finished with exit code 0

-删除

dic = {"a":1,"b":3}
v = dic.pop("a")
print(v)
print(dic)

运行结果：

1
{'b': 3}

Process finished with exit code 0

-随机删除

dic = {"a":1,"b":3}
v = dic.popitem()
print("删除的值为：",v)
print(dic)

运行结果：

删除的值为： ('b', 3)
{'a': 1}

Process finished with exit code 0

-设置，如果设置的值不存在，则创建新的，如果存在，不设置，直接获取当前的值

dic = {"a":1,"b":3}
v = dic.setdefault("c",132)
print(v)
print(dic)

运行结果：

132
{'a': 1, 'b': 3, 'c': 132}

Process finished with exit code 0

-添加

第一种方法：

dic = {"a":1,"b":3}
v = dic.update({"c":""})
print(dic)

运行结果：

{'a': 1, 'b': 3, 'c': ''}

Process finished with exit code 0

第二种方法：

dic = {"a":1,"b":3}
v = dic.update(c=123,d=456)
print(dic)

运行结果：

{'a': 1, 'b': 3, 'c': 123, 'd': 456}

Process finished with exit code 0