这是素数生成器pythonic吗 [英] is this primes generator pythonic

问题描述

下面的代码用于生成素数pythonic吗?

Is the following code for generating primes pythonic?

def get_primes(n):
    primes=[False,False]+[True]*(n-1)
    next_p=(i for i,j in enumerate(primes) if j)
    while True:
        p=next(next_p)
        yield p
        primes[p*p::p]=[False]*((n-p*p)//p+1)

请注意，next(next_p)最终将引发StopIteration错误，从而以某种方式结束函数get_primes.不好吗?

Note that next(next_p) will eventually throw a StopIteration error which somehow ends the function get_primes. Is that bad?

还要注意，next_p是一个生成器，它在素数上进行迭代，但是素数在迭代过程中会发生变化.那是不好的风格吗?

Also note that next_p is a generator which iterates over primes, however primes changes during iteration. Is that bad style?

添加以下if语句使前一百万个素数在0.25秒以下:

adding the following if statement gets it under 0.25 seconds for the first million primes:

if p*p<=n:
    primes[p*p::p]=[False]*((n-p*p)//p+1)

推荐答案

next(next_p)抛出StopIteration错误也不错-这是生成器在项目用完时始终会执行的操作！

It's not bad that next(next_p) throws a StopIteration error -- that's what a generator always does when it runs out of items!

在迭代列表时更改列表的长度是一个坏主意.但是，仅更改内容并没有错.总的来说，我认为这是一个相当优雅的(即使是基本的)诱惑.

Changing the length of a list while iterating over it is a bad idea. But there's nothing wrong with simply changing the contents. Overall, I think this is a rather elegant, if basic, seive.

一个小发现:当您划掉"质数的倍数时，如果仔细考虑一下，您会发现不必以p * 2开头.您可以跳到p ** 2.

One small observation: when you "cross out" the multiples of prime numbers, you'll find, if you think about it for a bit, that you don't have to start with p * 2. You can skip ahead to p ** 2.

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