Python 的 return 语句问题

问题描述

您好，我对 python 很陌生，想知道您是否可以帮我做点什么.我一直在玩弄这段代码，但似乎无法让它工作.

Hello I'm very new to python and was wondering if you could help me with something. I've been playing around with this code and can't seem to get it to work.

    import math

def main():
    if isPrime(2,7):
        print("Yes")
    else:
        print("No")

def isPrime(i,n):
    if ((n % i == 0) and (i <= math.sqrt(n))):
        return False
    if (i >= math.sqrt(n)):
        print ("is Prime: ",n)
        return True
    else:
        isPrime(i+1,n)
main()

现在 isPrime 方法的输出如下:

Now the output for the isPrime method is as follows:

is Prime:  7
No

我确定该函数应该返回 true，然后它应该打印是".我错过了什么吗?

I'm sure the function should return true then it should print "Yes". Am I missing something?

推荐答案

你正在丢弃递归调用的返回值:

You are discarding the return value for the recursive call:

def isPrime(i,n):
    if ((n % i == 0) and (i <= math.sqrt(n))):
        return False
    if (i >= math.sqrt(n)):
        print ("is Prime: ",n)
        return True
    else:
        # No return here
        isPrime(i+1,n)

你也想传播递归调用的值，包括一个 return 语句:

You want to propagate the value of the recursive call too, include a return statement:

else:
    return isPrime(i+1,n)

现在你的代码打印出来了:

Now your code prints:

>>> isPrime(2,7)
is Prime:  7
True

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