# Iterating through a range of dates in Python

### Question

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())
``````
• 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
``````

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 timedelta, date

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()`.

481
6/3/2015 10:35:18 AM

This might be more clear:

``````from datetime import date, timedelta

start_date = date(2019, 1, 1)
end_date = date(2020, 1, 1)
delta = timedelta(days=1)
while start_date <= end_date:
print (start_date.strftime("%Y-%m-%d"))
start_date += delta
``````