我的 For 循环不会遍历列表

问题描述

我必须确定列表中的所有数字是否都是素数，然后根据结果返回布尔真"或假"语句.我在 for 循环中做了一些条件语句来查看数字是否为素数.

I have to determine if all the numbers in a list are prime numbers and then return a boolean "True" or "False" statement depending on the outcome. I made some conditional statements inside of a for loop to see if the number was prime or not.

代码如下:

def all_primes(xs):
    is_prime = None
    for i in xs:
        if i < 2:
            is_prime = False
            return is_prime
            break
        elif (i % 2 == 0) and (i % i == 1):
            is_prime = False
            return is_prime
            break
        else:
            is_prime = True
            return is_prime

问题是，我在 Python Visualizer 中看到了这一点，for 循环在检查列表中的第一个值后停止迭代.我不明白为什么语法与我过去使用的 for 循环相同.

The problem is, and I saw this in the Python Visualizer, the for loop stops iterating after checking the first value in the list. I don't understand why as the syntax is the same as for loops I've used in the past.

我插入了一些示例值，例如:all_primes([5,2,11,37]) 或 all_primes([5,2,4,37])并且返回值始终为真，因为 5 是列表中的第一个数字，也是唯一被迭代的数字.

I plugged in some example values like: all_primes([5,2,11,37]) or all_primes([5,2,4,37]) and the return value is always true since 5 is the first number on the list and the only number that is being iterated.

关于为什么的任何想法?

Any ideas as to why?

推荐答案

你的 if/else 中有一个 return 和一个 break块，你应该摆脱它们.else 中的 return 也应该在外面，否则只要他找到素数"，它就会返回.

You have a return and a break in your if/else block, you should get rid of them. Also the return in the else should be outside, or it will just return whenever he finds a "prime".

def all_primes(xs):
  is_prime = None
  for i in xs:
      if i < 2:
          is_prime = False
          return is_prime
      elif (i % 2 == 0):
          is_prime = False
          return is_prime
      else:
          is_prime = True
  return is_prime

在此之后，您应该知道，您并没有真正检查素数.这不是最有效的方法，但它很清楚如何:

After this, you should know, that you are not really checking primes. Here is not the most efficient way but its clear how to:

def all_primes(xs):
    def checkPrime(n):
        if n < 2:
            return False
        for i in xrange(2, n):
            if n%i == 0:
                return False
        return True
    return all(map(checkPrime, xs))

如果没有 map 函数，您只需要使用 for 循环进行迭代:

without the map functions, you just have to iterate with a for loop:

def all_primes(xs):
    def checkPrime(n):
        if n < 2:
            return False
        for i in xrange(2, n):
            if n%i == 0:
                return False
        return True
    for n in xs:
        if not checkPrime(n):
            return False
    return True

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