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pythondatedatetimeiterationdate-range

Iterating through a range of dates in Python


I have the following code to do this, but how can I do it better? Right now I think it's better than nested loops, but it starts to get Perl-one-linerish when you have a generator in a list comprehension.

day_count = (end_date - start_date).days + 1
for single_date in [d for d in (start_date + timedelta(n) for n in range(day_count)) if d <= end_date]:
    print strftime("%Y-%m-%d", single_date.timetuple())

Notes

  • I'm not actually using this to print. That's just for demo purposes.
  • The start_date and end_date variables are datetime.date objects because I don't need the timestamps. (They're going to be used to generate a report).

Sample Output

For a start date of 2009-05-30 and an end date of 2009-06-09:

2009-05-30
2009-05-31
2009-06-01
2009-06-02
2009-06-03
2009-06-04
2009-06-05
2009-06-06
2009-06-07
2009-06-08
2009-06-09

Solution

  • Why are there two nested iterations? For me it produces the same list of data with only one iteration:

    for single_date in (start_date + timedelta(n) for n in range(day_count)):
        print ...
    

    And no list gets stored, only one generator is iterated over. Also the "if" in the generator seems to be unnecessary.

    After all, a linear sequence should only require one iterator, not two.

    Update after discussion with John Machin:

    Maybe the most elegant solution is using a generator function to completely hide/abstract the iteration over the range of dates:

    from datetime import date, timedelta
    
    def daterange(start_date, end_date):
        for n in range(int((end_date - start_date).days)):
            yield start_date + timedelta(n)
    
    start_date = date(2013, 1, 1)
    end_date = date(2015, 6, 2)
    for single_date in daterange(start_date, end_date):
        print(single_date.strftime("%Y-%m-%d"))
    

    NB: For consistency with the built-in range() function this iteration stops before reaching the end_date. So for inclusive iteration use the next day, as you would with range().