【Python】dict类方法汇总

注意字典中的元素是无序的

1 get() 根据key获取对应的值，key不存在默认取None

v = {
"k1":'v1', # 键值对
"k2":'v2', # 键值对
}

val = v.get('k1')
val2 =v.get('klffff','9999') #如果key不存在，则将设置为默认值，另默认值为None
val3 =v.get('k3333')
print(val)
print(val2)
print(val3)v1
9999
None

2 下面的方法是可与for循环一起使用

val=v.keys()
print(val)

val=v.values()
print(val)

val=v.items()
print(val)dict_keys(['k1', 'k2'])
dict_values(['v1', 'v2'])
dict_items([('k1', 'v1'), ('k2', 'v2')])

3 dict 类中的公共方法
（1）取长度
（2）根据索引修改，取值，删除值
（3）for循环
- for a in v.keys()
- for a in v.values():
- for a,b in v.items():

# v = {
# "k1":'v1', # 键值对
# "k2":'v2', # 键值对
# }

# 1. 获取字典长度（键值对的个数）
# val = len(v)
# print(val)

# 2. 索引
# - 获取
# val = v['k1'] # k1不存在会报错，v.get('k1') 也能取值，且不会报错
# print(val)

# -设置
# key存在，则更新值
# key不存在，则创建键值对
# v['kk1'] = 666

# - 删除
# del v['k1']

# 3. for循环
# v = {
# "k1":'v1', # 键值对
# "k2":'v2', # 键值对
# }
#
# for i in v:
# print(i)
# for i in v.keys():
# print(i)

# for i in v.values():
# print(i)


# key,value
# for i in v.keys():
# print(i,v[i]) # "k1"
# for a,b in v.items():
# print(a,b)

4 dict中的补充方法
（1）copy() deepcopy() 深浅拷贝

dic1 = {
'k1': 'v1',
'k2': [11,22,33,44]
}
dic2 = dic1.copy()
print(dic1,dic2)
dic1['k2'].append(666)
print(dic1,dic2)

dic1 = {
'k1': 'v1',
'k2': [11,22,33,44]
}
import copy
dic2 = copy.deepcopy(dic1)
print(dic1,dic2)
dic1['k2'].append(666)
print(dic1,dic2){'k1': 'v1', 'k2': [11, 22, 33, 44]} {'k1': 'v1', 'k2': [11, 22, 33, 44]}
{'k1': 'v1', 'k2': [11, 22, 33, 44, 666]} {'k1': 'v1', 'k2': [11, 22, 33, 44, 666]}
{'k1': 'v1', 'k2': [11, 22, 33, 44]} {'k1': 'v1', 'k2': [11, 22, 33, 44]}
{'k1': 'v1', 'k2': [11, 22, 33, 44, 666]} {'k1': 'v1', 'k2': [11, 22, 33, 44]}

（2）pop() 删除指定key 的键值对

dic = {'k1':'v1','k2':'v2'}
v = dic.pop('k23','默认值') #删除不存在字典中的key则为默认值，与list中pop方法类似
print(dic)
print(v){'k1': 'v1', 'k2': 'v2'}
默认值

（3）popitem() 注意字典无序，随机删除一个

dic = {'k1':'v1','k2':'v2'}
v1,v2 = dic.popitem()
print(dic)
print(v1,v2){'k1': 'v1'}
k2 v2

（4）setdefault()

dic = {'k1':'v1','k2':'v2'}
#添加
dic.setdefault('k2','999')
print(dic)
#设置：添加，修改,第二种方法
dic['k2'] = 999{'k1': 'v1', 'k2': 'v2'}

(5)update() 更新字典中的值

dic = {'k1':'v1','k2':'v2'} # dict类的一个对象
dic.update({'k4':'v4','k2':'v5'})
print(dic)'k1': 'v1', 'k2': 'v5', 'k4': 'v4'}

(6)fromkeys() 生成一个字典，不同的key中指向同一个地址

val = dict.fromkeys(['k1','k2','k3'],666)
print(val)
val['k1'] = 999
print(val)

val = dict.fromkeys(['k1','k2','k3'],[])
val['k1'].append(678)
val['k2'].append(999)
print(val)

val = dict.fromkeys(['k1','k2','k3'],[])
val['k1'].append(666)
val['k1'] = [1,2,3]
print(val){'k1': 666, 'k2': 666, 'k3': 666}
{'k1': 999, 'k2': 666, 'k3': 666}
{'k1': [678, 999], 'k2': [678, 999], 'k3': [678, 999]}
{'k1': [1, 2, 3], 'k2': [666], 'k3': [666]}