How to create Python Generator that iterates through date range giving me 3 day segments?

Question

I need to query an API for data over a multi-month period. However, the API chokes on longer than 3-day intervals.

So I want to create a generator function to separate my multi-month date range into 3 day segments that I can use while repeatedly calling my function that hits the API: When I pass it the start date and end date, it gives me:

the first time gives me start date,start date +3 days
next time gives me start date + 3 days, start date + 6 days
each time thereafter it moves forward by 3 day increments
until it hits the end date, when it gives me the days remaining to hit the end date if I still have 1 or 2 days left of data to grab
stops

Here's my code so far. It will work for the first time, but I'm not sure how to get the start date to increment by 3 days the next time I call the function. And I'm also not sure how if I still have 1 or 2 days left before hitting the final end date to set my until variable to the final end date--I think right now it simply says "there's less than 3 days left until the final date, so let's quit":

3_day_segmenter(start, end):
    start_date = datetime.strptime(start, '%Y-%m-%d')
    end_date = datetime.strptime(end, '%Y-%m-%d')
    since = start_date
    for date in range(int ((end_date - start_date).days)): 
        until = start_date + datetime.timedelta(days=3)     
        yield since, until

possible duplicate of [Generate a list of datetimes between an interval in python](http://stackoverflow.com/questions/10688006/generate-a-list-of-datetimes-between-an-interval-in-python) — Martijn Pieters, Oct 10 '13 at 22:22
That answer provides you with a generator that produces dates by a `timedelta` step size; it's trivial to turn that into something that also produces an end date. — Martijn Pieters, Oct 10 '13 at 22:24

score 5 · Accepted Answer · edited May 23 '17 at 11:59

Adapting Generate a list of datetimes between an interval to your needs:

from datetime import date, timedelta

def perdelta(start, end, delta):
    curr = start
    while curr < end:
        yield curr, min(curr + delta, end)
        curr += delta

This yields a (date1, date2) tuple that is constrained to the end date for the last segment:

>>> for s, e in perdelta(date(2011, 10, 10), date(2011, 11, 10), timedelta(days=3)):
...     print s, e
... 
2011-10-10 2011-10-13
2011-10-13 2011-10-16
2011-10-16 2011-10-19
2011-10-19 2011-10-22
2011-10-22 2011-10-25
2011-10-25 2011-10-28
2011-10-28 2011-10-31
2011-10-31 2011-11-03
2011-11-03 2011-11-06
2011-11-06 2011-11-09
2011-11-09 2011-11-10

Note that the last result covers only 2 days.

How to create Python Generator that iterates through date range giving me 3 day segments?

1 Answers1