for
1.当for后面接的是列表时，程序是怎样运行的？shoplist = ['apple', 'mango', 'carrot', 'banana']
print('I have', len(shoplist), 'items to purchase.')
print('These items are:', end=' ')
for item in shoplist:
print(item, end=' ')
2.当for后面接的是字典的键值对时，一定需要两个变量吗？
allguess={'1':{'apples':5,'pretzeles':12},
'2':{'ham sandwiches':3,'apples':2},
'3':{'cups':3,'apple pies':1}}
def a(guests,item):
numbrount=0
for k,v in guests.items():
numbrount=numbrount+v.get(item,0) 1.接列表时，是这样运行的：
依次从列表的第零个元素起直到最后一个元素分别赋值给变量，执行一次代码
2.接字典且变量只用一个时，变量迭代字典的键，如：di = {1:'one', 2:'two', 3:'three'}
for key in di:
print(key, di)
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