问题
This is a bit difficult to explain, so I apologize if this doesn't make much sense.
I have a program where I am doing some scheduling. One of the settings it has is to run a task weekly on certain days. For example, weekly on Monday, Wednesday and Friday.
Consider the example where the current task is scheduled for 1/2/2012, which is a Monday, I already have a bunch of code working to the point where I know the next task run should be on the wednesday following 1/2/2012. All I need to do is calculate the actual date of that Wednesday (1/4/2012).
I actually have the day of the week as the corresponding integer from date.weekday(), so in this case I have 2 which represents wednesday.
Whats the best way to handle something like this? I feel like there should be a fairly simple solution, but it isn't coming to mind. I was thinking of using a calendar object to search through to find the day of the week I want, but that seems like overkill.
回答1:
Use a timedelta to add to a date. For example, using some date d as the scheduled date for a current task, and some day next_day (the next day you'd like to run the task).
from datetime import date, timedelta
...
n = (next_day - d.weekday()) % 7 # mod-7 ensures we don't go backward in time
next_run_date = d + timedelta(days=n)
回答2:
Use dateutil.relativedelta:
from dateutil import relativedelta
import datetime
today = datetime.date.today()
# datetime.date(2012, 1, 3)
today + relativedelta.relativedelta(weekday=2) # 2 is Wednesday
# datetime.date(2012, 1, 4)
today + relativedelta.relativedelta(weekday=6) # 6 is Sunday
# datetime.date(2012, 1, 8)
today + relativedelta.relativedelta(weekday=1) # 1 is Tuesday
# datetime.date(2012, 1, 3)
# returns today
today + relativedelta.relativedelta(weeks=1, weekday=1)
# datetime.date(2012, 1, 10)
# returns Tuesday at least one week ahead
回答3:
We know that:
- from Monday to Wednesday there is 2 days of difference.
- from Wednesday to Friday there is 2 days of difference.
- from Friday to Monday there is 3 days of difference.
So, this is as simple as adding the days of difference between scheduled tasks:
from datetime import datetime, timedelta
first_scheduled_task = datetime(year=2012, month=1, day=2)
second_scheduled_task = first_scheduled_task + timedelta(2)
third_scheduled_task = second_scheduled_task + timedelta(2)
fourth_scheduled_task = third_scheduled_task + timedelta(3)
This would give us as result:
>>> first_scheduled_task
datetime.datetime(2012, 1, 2, 0, 0) # Monday 1/2/2012
>>> second_scheduled_task
datetime.datetime(2012, 1, 4, 0, 0) # Wednesday 1/4/2012
>>> third_scheduled_task
datetime.datetime(2012, 1, 6, 0, 0) # Friday 1/6/2012
>>> fourth_scheduled_task
datetime.datetime(2012, 1, 9, 0, 0) # Monday 1/9/2012
回答4:
Use dateutil for working with scheduling and recurrences.
来源：https://stackoverflow.com/questions/8708058/python-given-a-date-and-weekday-find-the-date-of-the-next-occurrence-of-a-given