python基础之字典篇

tips:字典是另一种可变容器模型，且可存储任意类型对象，字典是由键值对构成，键必须是不可迭代对象，值可以为任意对象

一，字典的声明与赋值

#声明一个字典
dict = {}
#字典初始化赋值
dict = {"name":"wuxiaoshi","major":"programmer"}

二，字典的查询

#读取字典
dict = {"name":"wuxiaoshi","major":"programmer"}
dict['name'] # wuxiaoshi
dict['major'] #programmer

#循环读取
for key,item in dict.items():
    print(item) # 值 wuxiaoshi,programmer
    print(key)  #键 name,major

三，字典的新增

# 字典的添加
dict = {}
dict['name'] = 'wuxiaoshi'
dict['age'] = 20
print(dict) #{"name":"wuxiaoshi","age":20}

#setdefault(key,value) 键无则添加 键有则不变，值无就是None
dict = {}
dict.setdefault('age',20)
dict.setdefault('name':'wuxiaoshi')
dict.setdefault('name':'xiaowushi')
dict.setdefault('hobbdy')
print(dict) # {'age': 20, 'name': 'wuxiaoshi', 'hobbdy': None}

四，字典的删除

#pop(key) 如果key存在，则删除key相应的这个键值对，并返回key对应的value,否则，将会报错 KeyError 
dict = {"name":"wuxiaoshi","age":20,"hobby":"reading,writting"}
print(dict.pop('name')) # wuxiaoshi
print(dict) #{'age': 20, 'hobby': 'reading,writting'}
print(dict.pop('a')) #  KeyError:a

#popitem() D.popitem() -> (k, v), remove and return some (key,value) pair as a 2-tuple; but raise KeyError if D is empty.
dict = {"name":"wuxiaoshi","age":20,"hobby":"reading,writting"}
print(dict.popitem()) # 理论上是随机删除一个，可能会有问题

#del 删除
dict = {"name":"wuxiaoshi","age":20,"hobby":"reading,writting"}
del dict['name'] #删除 name的键值对
del dict #删除整个字典，从内存中把空间抹掉

#clear 清空，但是保留内存地址
dict.clear()  # {}

五，字典的更新

# 直接更改方法
dict = {"name":"wuxiaoshi","age":20,"hobby":"reading,writting"}
dict['name'] = 'xiaowushi'
print(dict) #{'name': 'xiaowushi', 'age': 20, 'hobby': 'reading,writting'}

#update
'''
update(...) method of builtins.dict instance
    D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
    If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
    If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
    In either case, this is followed by: for k in F:  D[k] = F[k]
   翻译过来就是 有则更新，无则添加
'''
dict1 = {"name":"wuxiaoshi","age":20,"hobby":"reading,writting"}
dict2 = {"name":"furao","major":"programmer"}

dict1.update(dict2) # {'name': 'furao', 'age': 20, 'hobby': 'reading,writting', 'major': 'programmer'}

dict2.update(dict1) #{'name': 'wuxiaoshi', 'major': 'programmer', 'age': 20, 'hobby': 'reading,writting'}

六，字典的内置函数

# get()  通过Key来找值,如果key不存在，可以设置一个默认值
dict = {"name":"furao","major":"programmer"}

dict.get("name")  # furao
dict.get('age',18) # 18

#keys() 获取字典中的key 返回dict_keys
dict = {"name":"wuxiaoshi","age":20,"hobby":"reading,writting"}
dict.keys() # dict_keys(['name', 'age1', 'hobby']) 如果想返回列表 则list强转
list(dict.keys()) # ['name', 'age', 'hobby']

#values()
dict = {"name":"wuxiaoshi","age":20,"hobby":"reading,writting"}
dict.values() # ['wuxiaoshi', 20, 'reading,writting']

#items()
dict.items() # [('name', 'wuxiaoshi'), ('age1', 20), ('hobby', 'reading,writting')]