005---Python数据类型--字典

# 一
dic = {‘name‘:‘江子牙‘,‘age‘:21}
print(dic,type(dic))

# 二
dic1 = dict(name=‘江子牙‘,age=21)
print(dic1)

# 三
dic2 = {}
print(dic2,type(dic2))

# 增加

dic = {‘name‘:‘江子牙‘,‘age‘:21}

# 存在则修改，不存在，则添加
dic[‘sex‘] = ‘男‘
print(dic)

dic.setdefault(‘closed‘,‘停用‘)
print(dic)
# 存在key，不做任何改变。不存在则添加。
dic.setdefault(‘name‘,‘小喵喵‘)
print(dic)

# 删除
dic = {‘name‘: ‘江子牙‘, ‘age‘: 21, ‘sex‘: ‘男‘, ‘closed‘: ‘停用‘}

# 有返回值  没有key时就会报错  最好在后面加None
dic.pop(‘closed‘)  
print(dic)


# 随机删除  返回(key,value)  无意义
res = dic.popitem() 
print(res)
print(dic)

# del  不存在就会报错
del dic[‘name‘]
print(dic)

# clear()  清空字典
dic.clear()
print(dic)

dic1 = {‘name‘: ‘江子牙‘, ‘age‘: 21, ‘sex‘: ‘男‘, ‘closed‘: ‘停用‘}
print(dic1.pop(‘删除‘,‘不存在‘))
dic1.pop(‘删除‘)

# 总结：最好通过pop来删除 不存在时可以通过设置返回值还不会报错

# 改

# update()
d1 = {‘name‘:‘alex‘,‘age‘:18}
d2 = {‘name‘:‘‘,‘sex‘:1,‘age‘:22}
d2.update(d1)

# 覆盖添加
print(d2)

d2.update(name=1,age=2)
print(d2)

d2.update({‘sex‘:‘男‘})
print(d2)

# 查

d = {‘name‘: ‘江子牙‘, ‘age‘: 21, ‘sex‘: ‘男‘}
print(d.keys())    # 返回列表
print(d.values())  # 返回列表
print(d.items())   # 返回列表，里面是元祖

print(d.get(‘name‘))
print(d.get(‘aaa‘))
print(d.get(‘aaa‘,‘不存在‘))

# 可通过for循环来对上述结果来进行查询。

for key in d:
    print(key)
    
for key in d.keys():
    print(key)
    
for key,value in d.items():
    print(key,value)

总结：首选get