Python分段错误?

问题描述

这会生成一个Segmentation Fault: 11，我不知道为什么.

在开始学习之前，这里是代码:

import numpy.random as nprnd
import heapq
import sys

sys.setrecursionlimit(10**6)


def rlist(size, limit_low, limit_high):
    for _ in xrange(size):
        yield nprnd.randint(limit_low, limit_high)

def iterator_mergesort(iterator, size):
    return heapq.merge(
         iterator_mergesort(
           (iterator.__next__ for _ in xrange(size/2)), size/2),
         iterator_mergesort(
            iterator, size - (size/2))
       )

def test():
    size = 10**3
    randomiterator = rlist(size, 0, size)
    sortediterator = iterator_mergesort(randomiterator, size)
    assert sortediterator == sorted(randomiterator)

if __name__ == '__main__':
    test()

基本上，它只是一个用于迭代器和生成器表达式的合并排序，而不是用于列表的合并排序，以便一次最大程度地减少内存占用.没什么特别的，它使用内置的heapq.merge()合并迭代器的方法，所以当一切都中断时，我感到非常惊讶.

快速运行代码会给出Segmentation Fault: 11，并显示一个错误窗口，告诉我python崩溃了.我不知道在哪里寻找或如何调试它，所以我们将不胜感激.

解决方案

Segmentation Faults在python中发生的原因有两个:

您的内存不足了

插入C模块

此处，seg故障属于第一个.您(I)具有无限递归，因为iterator_mergesort()中没有基本情况，它将永远永远对自己进行调用.

通常，python为此抛出一个异常，它将在导致段错误之前终止.但是，递归限制已设置得非常高，因此python耗尽内存并在意识到它应该为无限制递归引发异常之前中断.

添加一个基本案例，如下所示:

...
def iterator_mergesort(iterator, size):
return heapq.merge(
         iterator_mergesort(
           (iterator.next() for _ in xrange(size/2)), size/2),
         iterator_mergesort(
            iterator, size - (size/2))
       ) if size >= 2 else iterator #<-- Specifically this

现在它通过了test()函数并进行了排序，尽管速度很慢.

This generates a Segmentation Fault: 11 and I have no clue why.

Before I get into it, here's the code:

import numpy.random as nprnd
import heapq
import sys

sys.setrecursionlimit(10**6)


def rlist(size, limit_low, limit_high):
    for _ in xrange(size):
        yield nprnd.randint(limit_low, limit_high)

def iterator_mergesort(iterator, size):
    return heapq.merge(
         iterator_mergesort(
           (iterator.__next__ for _ in xrange(size/2)), size/2),
         iterator_mergesort(
            iterator, size - (size/2))
       )

def test():
    size = 10**3
    randomiterator = rlist(size, 0, size)
    sortediterator = iterator_mergesort(randomiterator, size)
    assert sortediterator == sorted(randomiterator)

if __name__ == '__main__':
    test()

Basically, it's just a mergesort that works on iterators and generator expressions instead of working on lists so as to minimize the memory footprint at any one time. It's nothing special, and uses the heapq.merge() built-in method for merging iterators, so I was quite surprised when everything breaks.

Running the code quickly gives Segmentation Fault: 11 and an error window telling me python has crashed. I have no idea where to look or how to debug this one, so any help would be much appreciated.

解决方案

Segmentation Faults in python happen for one of two reasons:

You run out of memory

Bug in a C module

Here, the seg fault belongs to the first. You (I) have a boundless recursion because there is no base case in iterator_mergesort(), it'll keep calling itself on itself forever and ever.

Normally, python throws an exception for this and it will terminate before causing a segfault. However, the recursion limit has been set extremely high so python runs out of memory and breaks before it recognizes it should throw an exception for an unbounded recursion.

Add a base case like so:

...
def iterator_mergesort(iterator, size):
return heapq.merge(
         iterator_mergesort(
           (iterator.next() for _ in xrange(size/2)), size/2),
         iterator_mergesort(
            iterator, size - (size/2))
       ) if size >= 2 else iterator #<-- Specifically this

Now it passes the test() function and sorts, albeit rather slowly.

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