Python

Question

给定以下字符串列表

from datetime import datetime
import numpy as np


strings = ['Nov 1 2021', 'Oct 25 2021', 'Oct 18 2021', 'Oct 11 2021', 'Oct 4 2021', 'Sep 27 2021',
                'Sep 20 2021', 'Aug 24 2021', 'Aug 16 2021', 'Aug 9 2021', 'Aug 2 2021', 'Jul 26 2021',
                'Jun 28 2021', 'Jun 21 2021', 'Jun 14 2021', 'Jun 7 2021', 'May 24 2021', 'May 10 2021',
                'May 3 2021', 'Apr 26 2021', 'Apr 12 2021', 'Apr 12 2021', 'Apr 5 2021', 'Mar 22 2021',
                'Feb 22 2021', 'Feb 13 2021', 'Feb 8 2021', 'Feb 1 2021', 'Nov 2 2020', 'Sep 28 2020',
                'Aug 31 2020', 'Aug 20 2020', 'Aug 10 2020', 'Jun 29 2020', 'Jun 22 2020', 'Jun 15 2020',
                'Mar 2 2020', 'Feb 10 2020', 'Feb 3 2020', 'Jan 27 2020', 'Jan 20 2020', 'Jan 13 2020',
                'Jan 6 2020', 'Aug 26 2019', 'Aug 5 2019', 'Jul 29 2019', 'Jul 22 2019', 'Jul 15 2019']

return 列出过去 365 天内的日期的最有效方法是什么？

这是我失败的尝试：

# Converts strings to datetime format and appends to new list, 'dates.'

dates = []
for item in strings:
    convert_string = datetime.strptime(item, "%b %d %Y").date()
    dates.append(convert_string)


# Given each item in 'dates' list returns corresponding
# list showing elapsed time between each item and today (Nov 11th 2021).

elapsed_time = []
def dateDelta(i):
    today = datetime.fromisoformat(datetime.today().strftime('%Y-%m-%d')).date()
    date = i
    delta = (today - date).days
    elapsed_time.append(delta)

for i in dates:
    dateDelta(i)


# Concatenates 'dates' list and 'elapsed_times_list' in attempt to somehow connect the two.

date_and_elapsed_time = []
date_and_elapsed_time.append(dates)
date_and_elapsed_time.append(elapsed_time)


# Takes 'elapsed_time list' appends only the dates that fall within the last 365 days.

relevant_elapsed_time_list = []
for i in elapsed_time:
    if i <= 365:
        relevant_elapsed_time_list.append(i)


# Finds indices of 'relevant_elapsed_time_list' within last 365 days.
# After trawling Whosebug posts, I import numpy in an effort to help with indexing.
# My thinking is I can use the indices of the relevant elapsed times from the
# 'elapsed_time_list' and return the corresponding date from the 'dates' list.

relevant_elapsed_time_list_indices = []
for item in relevant_elapsed_time_list:
    indexes = []
    for index, sub_lst in enumerate(date_and_elapsed_time):
        try:
            indexes.append((index, sub_lst.index(item)))
        except ValueError:
            pass
    relevant_elapsed_time_list_indices.append(indexes)

relevant_elapsed_time_list_indices = np.array([[x[0][0], x[0][1]] for x in relevant_elapsed_time_list_indices])

此时，我还无法将 relevant_elapsed_time_list_indices 列表转换为 date_and_elapsed_time 中第一个子列表的相应索引。这样做的目的是隔离那些索引（即日期）。

解决这个问题最有效的方法是什么？

Answer 1

您可以使用 .strptime 将字符串转换为 datetime 对象，然后使用使用 timedelta 的条件列表理解来选择过去 365 天内的对象：

from datetime import datetime, timedelta

last_365_days = [s for s in strings if datetime.strptime(s, "%b %d %Y") + timedelta(days=365) >= datetime.today()]

或者您可以提前计算截止日期：

cutoff = datetime.today() - timedelta(days=365)
last_365_days = [s for s in strings if datetime.strptime(s, "%b %d %Y") >= cutoff]

last_365_days 的值应该是（今天）：

['Nov 1 2021', 'Oct 25 2021', 'Oct 18 2021', 'Oct 11 2021', 'Oct 4 2021',
 'Sep 27 2021', 'Sep 20 2021', 'Aug 24 2021', 'Aug 16 2021', 'Aug 9 2021',
 'Aug 2 2021', 'Jul 26 2021', 'Jun 28 2021', 'Jun 21 2021', 'Jun 14 2021',
 'Jun 7 2021', 'May 24 2021', 'May 10 2021', 'May 3 2021', 'Apr 26 2021',
 'Apr 12 2021', 'Apr 12 2021', 'Apr 5 2021', 'Mar 22 2021', 'Feb 22 2021',
 'Feb 13 2021', 'Feb 8 2021', 'Feb 1 2021']

Python - 给定日期列表（作为字符串），我们如何 return 只有那些落在过去 365 天内的日期？

Python - Given list of dates (as strings), how do we return only those that fall within last 365 days?

indexing

filtering

numpy

list