#處理鍵不在字典中的情況

#查詢字典中是否有某鍵，有則鍵值+1，無則創(chuàng)建新鍵，值+1

#常規(guī)方法：in 或 KeyError

dictionary={'first':1,'second':2}

key1='third'

if key1 in dictionary:

? ? count1=dictionary[key1]

else:

? ? count1=0

dictionary[key1]=count1+1

#簡化key1：

if key1 not in dictionary:

? ? dictionary[key1]=0

dictionary[key1]+=1

key2='forth'

try:

? ? count2=dictionary[key2]

except KeyError:

? ? count2=0

dictionary[key2]=count2+1

#簡化key2

try:

? ? dictionary[key2]+=1

except KeyError:

? ? dictionary[key2]=1

#get方法 第一個參數為想查詢的鍵，第二個參數是鍵不存在時返回的默認值

key3='fifth'

count3=dictionary.get(key3,0)

dictionary[key3]=count3+1

print(dictionary)

#如果字典保存的數據類型比較復雜，如list

dictionaries={'first':['a','A'],'second':['b','B']}

key1='third'

value1='c'

value2='C'

if key1 in dictionaries:

? ? list1=dictionaries[key1]

else:

? ? dictionaries[key1]=list1=[]#完成空白列表賦給list1，并與key1關聯(lián)

list1.append(value1)

try:

? ? list2=dictionaries[key1]

except KeyError:

? ? dictionaries[key1]=list2=[]

list2.append(value2)

#用get改寫

key2='forth'

value3='d'

value4='D'

list3=dictionaries.get(key2)

if list3 is None:

? ? dictionaries[key2]=list3=[]

list3.append(value3)

#加上海象運算符

if(list4:=dictionaries.get(key2)) is None:

? ? dictionaries[key2]=list4=[]

list4.append(value4)

#setdefault方法

#查詢字典里是否有某鍵有則返回值，無則將提供的默認值此鍵關聯(lián)并插入字典

key='wsz'

name=dictionaries.setdefault(key,[])

name.append('nb')

print(dictionaries)