【Python】dict类方法汇总（python里的dict）

【Python】dict类方法汇总（python里的dict）

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Noneval3 =v.get('k3333')print(val)print(val2)print(val3)

v19999None

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 copydic2 = 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'] = 999print(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]}

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