在Python中使用列表推导查找最小/最大日期 [英] Finding Min/Max Date with List Comprehension in Python

问题描述

所以我有这个列表:

snapshots = ['2014-04-05',
        '2014-04-06',
        '2014-04-07',
        '2014-04-08',
        '2014-04-09']

我想使用列表理解来查找最早的日期.

I would like to find the earliest date using a list comprehension.

这里是我现在拥有的，

earliest_date = snapshots[0]
earliest_date = [earliest_date for snapshot in snapshots if earliest_date > snapshot]

当我打印最早的日期时，我期望返回一个空数组，因为列表的第一个元素之后的所有值已经大于第一个元素，但是我想使用一个值.

When I print the earliest date, I expect an empty array back since all the values after the first element of the list are already greater than the first element, but I WANT a single value.

这是原始代码，只是表示我知道如何查找最小日期值:

Here's the original code just to signify i know how to find the min date value:

for snapshot in snapshots:
    if earliest_date > snapshot:
        earliest_date = snapshot

有人有什么想法吗?

推荐答案

只需使用 min()或 max()查找最早或最新日期:

Just use min() or max() to find the earliest or latest dates:

earliest_date = min(snapshots)
lastest_date = max(snapshots)

当然，如果您的日期列表已经排序，请使用:

Of course, if your list of dates is already sorted, use:

earliest_date = snapshots[0]
lastest_date = snapshots[-1]

演示:

>>> snapshots = ['2014-04-05',
...         '2014-04-06',
...         '2014-04-07',
...         '2014-04-08',
...         '2014-04-09']
>>> min(snapshots)
'2014-04-05'

通常来说，列表理解只能用于构建列表，而不能用作常规循环工具.实际上，这就是 for 循环的用途.

Generally speaking, a list comprehension should only be used to build lists, not as a general loop tool. That's what for loops are for, really.

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