Question

正在打印“在使用list（zip_shop）之前，您好”语句。

“使用list（zip_shop）后，您好”语句未打印。

groceries = ["apple","chips","bread","icecream"]
price = [2,3,1.2,4.25]
print("groceries = ",groceries,"and price =",price)

zip_shop = zip(groceries,price)

print("zip_shop =", zip_shop,"and type(zip_shop) =",type(zip_shop),"and id(zip_shop) = ",id(zip_shop))
for g, p in zip_shop:
    print("Hello before using list(zip_shop)")


print("list(zip_shop)=", list(zip_shop),"and type(zip_shop) =",type(zip_shop),"and id(zip_shop) = ",id(zip_shop))
for g, p in zip_shop:
    print("Hello after using list(zip_shop)")

有人可以帮我理解这里的行为吗？

输出如下：

groceries =  ['apple', 'chips', 'bread', 'icecream'] and price = [2, 3, 1.2, 4.25]
zip_shop = <zip object at 0x0000022852A29948> and type(zip_shop) = <class 'zip'> and id(zip_shop) =  2372208335176
Hello before using list(zip_shop)
Hello before using list(zip_shop)
Hello before using list(zip_shop)
Hello before using list(zip_shop)
list(zip_shop)= [] and type(zip_shop) = <class 'zip'> and id(zip_shop) = 2372208335176

Process finished with exit code 0

Answer 1

在Python 3中，zip函数产生一个迭代器，该迭代器只能被使用一次，您必须将其转换为list：

zip_shop = list(zip(groceries, price))

Answer 2

您以错误的方式使用了zip对象。对Zip对象迭代器进行延迟计算，这意味着仅在调用它们时才对它们进行评估，而不会进行多次评估，这避免了对zip对象的重复评估。要进行迭代，必须为迭代对象调用Zip（）。

groceries = ["apple","chips","bread","icecream"]
price = [2,3,1.2,4.25]
print("groceries = ",groceries,"and price =",price)

#zip_shop = zip(groceries,price)

for g, p in zip(groceries,price):
    print("Hello before using list(zip_shop)")

print("List:",list(zip(groceries,price)))

for g, p in zip(groceries,price):
    print("Hello after using list(zip_shop)")

for循环中的语句在使用“ list（zip_variable）”之后不会被打印，但是在使用“ list（zip_variable）”之前会被打印

2 个答案: