如何检查列表是否已排序? [英] How do I check if a list is sorted?

问题描述

可能重复:
用Python方式检查列表是否已排序或不是

Possible Duplicate:
Pythonic way to check if a list is sorted or not

在python中，如何测试数字列表是否已排序?

In python, how do I test whether a list of numbers is already sorted or not?

推荐答案

这只能通过遍历列表(隐式或显式)来实现:

This is only possible by iterating over the list (implicitly or explicitly):

all(b >= a for a, b in zip(the_list, the_list[1:])

但是，如果需要对它进行排序，为什么不对它进行排序呢?在已经排序的列表上，Python的排序算法将非常便宜-可能比上面的测试便宜.

But why not just sort it if you need it to be sorted? Python's sorting algorithm will be really cheap on an already sorted list -- possibly cheaper than the test above.

因为这变成了关于性能的讨论，所以这里是使用惰性迭代器的版本:

Because this turned into a discussion about performance, here is a version using lazy iterators:

it = iter(the_list)
it.next()
all(b >= a for a, b in itertools.izip(the_list, it))

对于具有一百万个条目的随机排序列表，这比the_list == sorted(the_list)快10000倍以上.

For a randomly ordered list with a million entries, this is more than 10000 times faster than the_list == sorted(the_list).

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