Python 字典方法(.get .item)


allGuests={'Alice':{'apples':5,'pretzels':12},
           'Bob':{'ham sandwiches':3,'apples':2},
           'Carol':{'cups':3,'apple pies':1}}
def totalBrought(guests,item):#定義函數中兩個變量
    numBrought=0
    for k,v in guests.items():# 遍歷字典列表
        numBrought=numBrought+v.get(item,0)#返回指定鍵(item)的值
    return numBrought
print('Number of things being brought:')
print(' - Apples '+str(totalBrought(allGuests,'apples')))
print(' - cups '+str(totalBrought(allGuests,'cups')))
print(' - Cakes '+str(totalBrought(allGuests,'cakes')))
print(' - Ham Sandwiches '+str(totalBrought(allGuests,'ham sandwiches')))
print(' - apple Pies '+str(totalBrought(allGuests,'apple pies')))

dict.items()

把字典中每對 key 和 value 組成一個元組,並把這些元組放在列表中返回
dict = {'one': 1, 'two': 2, 'three': 3}

for a,b in dict.items()#兩個參數分別對應元祖中兩個元素
print(key + ':' + str(value))
one:1
two:2
three:3

for i in d.items():#當參數只有一個時
print(i)
('one', 1)
('two', 2)
('three', 3)

dict.get(key, default=None)

尋找dict中指定key的value

展開過程

num=0
K=Alice,V={'apples':5,'pretzels':12}
num=0+{'apples':5,'pretzels':12}.get(apples,0)
num=0+5
num=5
K=Bob,V={'ham sandwiches':3,'apples':2}
num=5+{'ham sandwiches':3,'apples':2}.get(apples,0)
num=5+2
num=7
K=Carol,V={'cups':3,'apple pies':1}
num=7+{'cups':3,'apple pies':1}.get(apples,0)
num=7+0
num=7
return num
num=7


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