Five, the function of the dictionary

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The dictionary is composed of each set of key-value pairs. Each key-value pair is relational data, and the query speed is very fast. Search by binary method

dic = {'key'：'value'，'name':'yy','hobby':'heheh','list':[2,3,'ee']，2：True

....}

Another way of categorizing data types

Mutable data types (non-hashable classes): list, dict, set

Immutable data type (hashable class): str int bool tuple

Container type (carries various data types): list dic tuple

Addition, deletion, modification and lookup of dictionary

The keys of a dictionary are unique, and there cannot be two identical keys in a dictionary

The order of the dictionary: unordered before 3.5, ordered after 3.6 (insert in a certain order when creating a dictionary, it looks ordered)

Addition, deletion and modification of dictionaries. check

1. Hash table Each dictionary has a hash table to locate each key-value pair through the hash table for easy lookup

dic = {'key':'value','name':'yy','hobby':'heheh','list':[2,3,'ee'],2:True}
print(hash('key'))
print(hash('value'))

#-2335181179344269333
#5043510051693866644

Each key-value pair has a hash number, and the hash value is constantly changing

dictionary addition

The first one: Overwrite if there is, add if not

dic = {'key':'value','name':'yy','hobby':'heheh','list':[2,3,'ee'],2:True}
dic['姓名'] = '张三'
dic['key'] = 'hehe'
print(dic)
#{'list': [2, 3, 'ee'], 2: True, 'name': 'yy', '姓名': ['张三'], 'key': 'value', 'hobby': 'heheh'}
#{'list': [2, 3, 'ee'], 'key': 'hehe', 2: True, 'name': 'yy', 'hobby': 'heheh'}

The second setdefault is added if there is no change

dic = {'key':'value','name':'yy','hobby':'heheh'}
dic.set.default('key','大炮')
dic.set.default('sex','femal')
print(dic)

# dic = {'key':'value','name':'yy','hobby':'heheh'}
# dic = {'key':'value','name':'yy','sex':'femal',hobby':'heheh'}  也是无序的增加进去
第三种  update
dic1.update(dic2)
将dic2中的键值对加入到dic1中，如果dic2中的键和dic1中的重复，则用dic2中的值覆盖dic1中的值 反之亦然
字典的删除

dic = {'key':'value','name':'yy','hobby':'heheh'}
第一种： pop 有返回值
print（dic.pop('key'）  只能删除键   打印的结果会是这个键对应的值  如果删除值 会报错
# value 
print（dic.pop('sex',None）  如果你要删除的键在这个字典中不存在，这种会返回你设定的值None  如果不设置的话 会报错
#  None  
第二种： clear
直接清空整个字典 留下空的字典
dic.clear()
print(dic)
#{}
第三种：del

dic = {'key':'value','name':'yy','hobby':'heheh'}

del dic
print（dic）
报错
del dic['key']          只能通过键来删除值   如果删除的是值 会报错

print(dic)
#{'name':'yy','hobby':'heheh'}

第四种：popitem         这是个逗比功能 随机删除字典中的键值对 但是可以返回
 print（dic.popitem()）

 字典的查

dic = {'key':'value','name':'yy','hobby':'heheh'}


第一种：通过键来查值  
print(dic['key']}

# value

第二种：get 通过键来查找值

print(dic.get('key')

#value

print(dic.get('sex'，'你要查找的没有')) 如果要查找的键不存在则默认返回None 如果自己定义了参数则返回你定义的

#你要查找的没有

其他方法 C

dic.values() 把字典的键值对中的值单独拉出来组成一个数据类型为dic_values的（[]）

print(dic.values()) dict_values(['heheh', 'value', 'yy'])

dic.keys() 把字典的键值对中的键单独拉出来组成一个数据类型为dic_key的（[]）

print(dic.keys()) dict_keys(['name', 'hobby', 'key'])

dic.items() 把字典的键值拉出来组成一个数据类型为dic_items的（[]）

print(dic.items()) dict_items([('key', 'value'), ('name', 'yy'), ('hobby', 'heheh')])

以上三种方法得出来的数据类型只能循环但是可以转换为列表的数据类型

分别赋值这个很有意思

a,b = 2,3

print(a,b)

#a = 3

b = 2 一行代码把a b 的值互换

（a,b）= (2,3)

print(a,b) # 2,3

dic = {'key':'value','name':'yy','hobby':'heheh'}
for x,y in dic.items():
    print(x,y)

#hobby heheh
name yy
key value

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Five, the function of the dictionary

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