Question

我有解决这个问题的方法，但我想知道它为什么会出问题。在下面的代码中，filter函数是一个unicode字符串列表，而不是is_date_string生成的datetime对象

import re
import requests

datestrings = re.compile(r'\d*-\d*-\d* \d*:\d*:\d*')

def is_date_string(s):
    try:
        return datetime.datetime.strptime(s, '%Y-%m-%d %H:%M:%S')
    except:
        return False

d = filter(is_date_string,datestrings.findall(request.text))

这是正则表达式产生的数据样本：

 DATESTRINGS = 
    [u'2016-06-24 05:36:42', u'2016-06-24 04:53:02', u'2016-06-24 04:53:02', u'2016-06-24 04:53:02', u'2016-06-24 04:53:02', u'2016-06-24 04:53:02', u'2016-06-24 04:53:02', u'2016-06-24 04:53:03', u'2016-06-24 04:53:04', u'2016-06-24 04:53:04', u'2016-06-24 04:53:04', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:05', u'2016-06-24 04:53:', u'2016-06-24 05:18:56', u'2016-06-24 05:36:43', u'2016-06-27 05:00:00']

我的工作是d的列表理解，以执行函数应该做的事情

dates = [datetime.datetime.strptime(x, '%Y-%m-%d %H:%M:%S') for x in d if x]

但是问题是关于is_date_string函数没有返回datetime对象。为什么呢？

Answer 1

过滤器使用函数的结果进行过滤，但返回是iterable的子集，在您的情况下是一个字符串。

你想要的东西似乎是这样的

d = filter(None, map(is_date_string,datestrings.findall(request.text)))

https://docs.python.org/2/library/functions.html#filter 来自doc

请注意，如果函数不是[item for item in iterable if function(item)]，则过滤器（函数，可迭代）等效于None，如果函数是[item for item in iterable if item]，则过滤器等效于None。

Python函数返回uncode字符串而不是datetime对象

1 个答案: