使用“list(zip_variable)”后没有打印for循环中的语句

Question

正在打印语句“Hello before using list(zip_shop)”。

语句“您好，使用 list(zip_shop)”后没有打印出来。

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，该zip函数产生一个迭代器，它只能被消耗一次，你必须将它转换为 a&nbsp;list：zip_shop&nbsp;=&nbsp;list(zip(groceries,&nbsp;price))

Answer 2

您以错误的方式使用 zip 对象。Zip 对象迭代器是惰性求值的，这意味着它们仅在被调用时才求值，不会被求值多次，这避免了对 zip 对象的重复求值。当您想要迭代时，您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):&nbsp; &nbsp; print("Hello before using list(zip_shop)")print("List:",list(zip(groceries,price)))for g, p in zip(groceries,price):&nbsp; &nbsp; print("Hello after using list(zip_shop)")