4.4 数据类型内置方法_可变类型(2)_字典

4.4 数据类型内置方法_可变类型(2)_字典

4.4.1 字典类型

1. 作用：列表存储元素过多，存取困难，所以引入字典；key对值一般具有描述意义，value可以是任意数据类型的值。

2. 定义方式：{}内以键值对：'key:value'的形式存储多个值

3. 方法：

• 方法1***

#(1)按key存取值可以存可以取
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
print(f'操作前：id:{id(info)},info:{info}')

info['height']+=1
info['age']=25
print(info)


print(f'操作后：id:{id(info)},info:{info}')

操作前：id:1603351003456,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}
{'name': 'coco', 'height': 186, 'weight': 140, 'hobby_list': ['read', 'run', 'run'], 'age': 25}
操作后：id:1603351003456,info:{'name': 'coco', 'height': 186, 'weight': 140, 'hobby_list': ['read', 'run', 'run'], 'age': 25}

#(2)长度len
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
print(len(info))

4

#(3)成员运算 in/not in,比较的是key
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}

print('height' in info)

True

#(4)del 删除
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
print(f'操作前：id:{id(info)},info:{info}')

del info['height']

print(f'操作后：id:{id(info)},info:{info}')

操作前：id:1603351232256,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}
操作后：id:1603351232256,info:{'name': 'coco', 'weight': 140, 'hobby_list': ['read', 'run', 'run']}

#(5)keys(),输出所有key
# values(),输出所有值
# items()，输出所有键值对
#把所有输出值当成列表
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}

print(info.keys(),type(info.keys()))

print(info.values())
print(info.items())

dict_keys(['name', 'height', 'weight', 'hobby_list']) <class 'dict_keys'>
dict_values(['coco', 185, 140, ['read', 'run', 'run']])
dict_items([('name', 'coco'), ('height', 185), ('weight', 140), ('hobby_list', ['read', 'run', 'run'])])

#(6)循环
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}

for i in info:
    print(i) #输出key
print('-'*100)
for i in info.values():
    print(i)
print('-'*100)

for i in info.items():
    print(i) #以元组形式输出
print('-'*100)

for i,j in info.items():
    print(i,j) #解压缩
print('-'*100)

name
height
weight
hobby_list
----------------------------------------------------------------------------------------------------
coco
185
140
['read', 'run', 'run']
----------------------------------------------------------------------------------------------------
('name', 'coco')
('height', 185)
('weight', 140)
('hobby_list', ['read', 'run', 'run'])
----------------------------------------------------------------------------------------------------
name coco
height 185
weight 140
hobby_list ['read', 'run', 'run']
----------------------------------------------------------------------------------------------------

• 方法2 **

#(1)get(key) 如果key不存在,返回none，不会报错
# get(key,x) key不存在用给定默认值x填充
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
print(f'操作前：id:{id(info)},info:{info}')

 
print('-'*100)
print(info.get('height'))
print(info.get('heigh','f'))

print(f'操作后：id:{id(info)},info:{info}')

操作前：id:1603351023296,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}
----------------------------------------------------------------------------------------------------
185
f
操作后：id:1603351023296,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}

#(2)update,有就更新，没有就追加。
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
print(f'操作前：id:{id(info)},info:{info}')

dict={'a':'A','b':'B','c':'C','weight':150}
info.update(dict)


print(f'操作后：id:{id(info)},info:{info}')

操作前：id:1603351025344,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}
操作后：id:1603351025344,info:{'name': 'coco', 'height': 185, 'weight': 150, 'hobby_list': ['read', 'run', 'run'], 'a': 'A', 'b': 'B', 'c': 'C'}

#(3)fromkeys(list,x),不常用
# 将list内的·元素当成键，取出来用x赋值不改变原来的字典
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
print(f'操作前：id:{id(info)},info:{info}')

print('-'*100)
info.fromkeys([1,2,3],5)
print(info.fromkeys([1,2,3],5))
print('-'*100)
print(info.fromkeys(['name','height'],5))
print('-'*100)

print(f'操作后：id:{id(info)},info:{info}')

操作前：id:1603351033152,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}
----------------------------------------------------------------------------------------------------
{1: 5, 2: 5, 3: 5}
----------------------------------------------------------------------------------------------------
{'name': 5, 'height': 5}
----------------------------------------------------------------------------------------------------
操作后：id:1603351033152,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}

#(4)setdefault,
# 如果字典中有该key的话，则key对应值不变；没有则追加，改变原来字典。
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
print(f'操作前：id:{id(info)},info:{info}')

print('-'*100)
info.setdefault('a','A')
print(info)
print('-'*100)

info.setdefault('height','A')

print(info)

print('-'*100)
print(f'操作后：id:{id(info)},info:{info}')

操作前：id:1603351026240,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run']}
----------------------------------------------------------------------------------------------------
{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run'], 'a': 'A'}
----------------------------------------------------------------------------------------------------
{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run'], 'a': 'A'}
----------------------------------------------------------------------------------------------------
操作后：id:1603351026240,info:{'name': 'coco', 'height': 185, 'weight': 140, 'hobby_list': ['read', 'run', 'run'], 'a': 'A'}

#(5)pop运算
info={'name':'coco',
      'height':185,
      'weight':140,
      'hobby_list':['read','run','run']}
info.pop()

4. 存储一个值或多个值：多个值，值可以是多个类型，key是不可变类型，通常是字符串。
5. 有序 or 无序：无序，按键取值
6. 可变or不可变：可变