python字典的创建，增删查改和字典的循环遍历

字典

字典特点

符号为大括号
数据为键值对形式出现
各个键值对用逗号隔开

dict1 = {'name':'TOM','age':20,'gender':'男'}
print(dict1)
print(type(dict1))
#有数据字典

#空字典
dict2 = {}
dict3 = dict()

字典新增

字典序列[key]=值

dict1 = {'name':'TOM','age':20,'gender':'男'}
dict1['id'] = 110
print(dict1)
#{'name': 'TOM', 'age': 20, 'gender': '男', 'id': 110}

dict1 = {'name':'TOM','age':20,'gender':'男'}
dict1['id'] = 110
dict1['name'] = 'Rose'
print(dict1)
#{'name': 'Rose', 'age': 20, 'gender': '男', 'id': 110}

如果key存在，则更新原字典值，不存在，则新增

删除

del()/del .clear删除字典或指定键值对

dict1 = {'name':'TOM','age':20,'gender':'男'}
del(dict1)#删除字典
del dict1['name']#删除键值对
dict1.clear()#清空字典

修改

字典序列[key] = 值

dict1 = {'name':'TOM','age':20,'gender':'男'}
dict1['name'] = 'Rose'

和修改相同，区别为看原字典是否存在key值

查找

key查找

dict1 = {'name':'TOM','age':20,'gender':'男'}
print(dict1['name'])  #TOM
print(dict1['id'])#报错

get()

dict1 = {'name':'TOM','age':20,'gender':'男'}
print(dict1.get('name')) #TOM
print(dict1.get('namesssss'))#key不存在，返回none
print(dict1.get('id',1100))#key不存在，返回设置值1100
print(dict1.get('id'))#key不存在，返回默认值none

keys()

dict1 = {'name':'TOM','age':20,'gender':'男'}
print(dict1.keys())#dict_keys(['name', 'age', 'gender'])#查找字典中所有的key,返回可迭代对象

values()

dict1 = {'name':'TOM','age':20,'gender':'男'}
print(dict1.values())#dict_values(['TOM', 20, '男'])#查找字典中所有的value,返回可迭代对象

items()

dict1 = {'name':'TOM','age':20,'gender':'男'}
print(dict1.items())#dict_items([('name', 'TOM'), ('age', 20), ('gender', '男')])
# #查找字典中所有的键值对,返回可迭代对象，里面的数据是元组

字典的循环遍历

遍历字典的key

dict1 = {'name':'TOM','age':20,'gender':'男'}
for key in dict1.keys():
    print(key)
#name
# age
# gender

遍历字典的value

dict1 = {'name':'TOM','age':20,'gender':'男'}
for value in dict1.values():
    print(value)
# TOM
# 20
# 男

遍历字典的元素

dict1 = {'name':'TOM','age':20,'gender':'男'}
for item in dict1.items():
    print(item)
# ('name', 'TOM')
# ('age', 20)
# ('gender', '男')

遍历字典的键值对

dict1 = {'name':'TOM','age':20,'gender':'男'}
for key,value in dict1.items():
    print(f'{key} = {value}')
# name = TOM
# age = 20
# gender = 男
#xx.items():返回可迭代对象，内部是元组，有两个元素
#元组数据1是字典的key,元组数据2是字典的value