Python:素数和inrange() [英] Python: Prime numbers and the in range()

问题描述

我正在学习python并正在研究此问题: Python-素数练习 这是我的问题: 当n = 2时，范围为(2，n)，换句话说，范围在2到2-1 = 1之间.

I am learning python and was looking at this problem: Python - Prime Number exercise Here are my questions: When n=2, the range will be (2,n), in the other words the range is between 2 and 2-1=1.

   for x in range(2, n):
      if n % x == 0:
        print("{} equals {} x {}".format(n, x, n // x))
        return False
   else:
      print(n, "is a prime number")
      return True

a.会是2％2吗?

b.如果数字是偶数，它将打印

b. If the number is even, it will print

A等于B x C

A equals B x C

条件成立时，循环会中断吗?还是会结束循环?

will the loop break once the condition is true or it will finish the loop?

c.循环之外的其他东西吗? if语句对应什么? (我知道它是if n % x == 0:)，但是看起来好像在循环之外呢? 我试图运行它，并且理解了，但是后来我感到困惑.

c. is the else outside the loop? what if statement does it correspond? (i know it is the if n % x == 0:) but howcome it is seems like it is outside the loop? I tried to run it, and understand, but then I got confused.

推荐答案

for .. else混乱

您似乎对for循环的一部分else感到困惑.

for .. else confusion

You seem to be confused by else which is part of the for loop.

您不是唯一的一个人.

在Python中，除非存在break语句，否则for循环可能在else节的末尾，该节在所有循环完成后才执行.是的，不是很直观.

In Python, for loop might have at the end else section, which is executed after all the loops are finished, unless there was break statement. Yes, it is not very intuitive.

因此，您应该在for循环的最后部分阅读else部分.

So you shall read the else section as last part of the for loop.

def looptest(loops=5):
    for i in range(loops):
        print "i", i
        if i == 3:
            print "in if"
            return
    else:    
        print "in else of the loop"

并尝试循环== 5:

>>> looptest(5)
i 0
i 1
i 2
i 3
in if

对于循环2的数量，我们不希望返回，我们将在循环的else中运行:

For number of loops 2 we do not expect return, we shall run through else of the loop:

>>> looptest(2)
i 0
i 1
in else of the loop

请注意，return必须在函数内，尝试在控制台上返回会导致错误.

Note, that return must be within function, trying return on console would result in error.

在Python控制台上尝试:

Trying on Python console:

>>> range(2, 2)
[]

返回

return结束当前功能或在整个模块中运行.因此，在return之后，将不再执行代码同一部分中的其他代码(try，finally，上下文管理器等例外，但这与您的代码无关).

return

return ends up current function or run in the whole module. So after return, no further code in the same part of your code is executed (with exceptions like try, finally, context managers etc, but this is not relevant to your code).

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