python学习笔记之基础操作（三）元组列表字典（4）字典常用方法

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#fromkeys 返回一个字典，所有的value都被初始化为一个值
dic = dict.fromkeys([1,2,3,4,5],True)
print(dic)
dic = dict.fromkeys([1,2,3,4,5],["a","b"])
print(dic)
dic = dict.fromkeys([1,2,3],{1:'a',2:'b',3:'c'})
print(dic)

{1: True, 2: True, 3: True, 4: True, 5: True}
{1: ['a', 'b'], 2: ['a', 'b'], 3: ['a', 'b'], 4: ['a', 'b'], 5: ['a', 'b']}
{1: {1: 'a', 2: 'b', 3: 'c'}, 2: {1: 'a', 2: 'b', 3: 'c'}, 3: {1: 'a', 2: 'b', 3: 'c'}}

#get()得到对应键的值
dic = {1:'a',2:'b',3:'c'}
print(dic.get(2))

b

#items:返回一个键值对
for item in dic.items():
    print(item)

(1, 'a')
(2, 'b')
(3, 'c')

#key，values，返回值为相应的数据
print(dic.keys())
print(dic.values())

dict_keys([1, 2, 3])
dict_values(['a', 'b', 'c'])

#update:按照键更新数据，对于已经存在的键直接更新，不存在的则添加新数据
dic = {1:'a',2:'b',3:'c'}
print(dic)
t={1:'z',2:'z',4:'z'}
dic.update(t)
print(dic)

{1: 'a', 2: 'b', 3: 'c'}
{1: 'z', 2: 'z', 3: 'c', 4: 'z'}