Python将列表中的所有偶数相乘 [英] Python multiplying all even numbers in a list

问题描述

我正在为我的第一个编程课程编写此python代码.昨天它部分起作用，但是后来我做了一些更改，现在仅通过了1个测试用例.目标是将列表"xs"中的所有偶数相乘，如果没有偶数则返回1.我在做什么错，我该如何解决?

I am working on this python code for my first programming class. Yesterday it partially worked but then I changed something and now it is only passing 1 test case. The goal is to multiply all even numbers in list "xs" and return 1 if there are no even numbers. What am I doing wrong and how can I fix it?

def evens_product(xs):
    product = 2
    for i in xs:
        if i%2 == 0:
            product *= i
            return product

    else:
        return (1) 

Chepner的解决方案对所有帮助过的人都表示感谢

Chepner's solution worked thank you to everyone who helped

推荐答案

由于两个原因，您需要初始化product = 1.一种，简单地说，您会得到错误的答案. evens_product([4])应该返回4，而不是8. 第二，它使您不必将没有偶数的列表作为特例.如果没有偶数，则永远不要更改product的值并将其保持不变.

You need to initialize product = 1, for two reasons. One, simply put, you'll get the wrong answer. evens_product([4]) should return 4, not 8. Two, it saves you from having to treat a list with no even numbers as a special case. If there are no even numbers, you never change the value of product and return it unchanged.

def evens_product(xs):
    product = 1
    for i in xs:
        if i%2 == 0:
            product *= i
    return product

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