Generate list of months between interval in python

Question

I want to generate a python list containing all months occurring between two dates, with the input and output formatted as follows:

date1 = \"2014-10-10\"  #         


        

Answer 1

Having done similar stuff previously, I took a stab at solving this. Using distinct components for doing this is more flexible and enables you to mix and match them for different use-cases. They also can be tested more easily this way, as you can see by the doctests in iterate_months.

Also I suggest to use datetime.date objects for your input as you can just do more with those. To do that you'll have to first parse your input string, but this is very easily done.

Parsing the date-strings

def datify(date):
    if isinstance(date, datetime.date):
        return date
    elif isinstance(date, datetime.datetime):
        return date.date()
    else:
        # taken from simleo's answer
        return datetime.strptime(date, "%Y-%m-%d")

First, we iterate through the months

import datetime


def iterate_months(start_date, end_date):
    """Iterate monthly between two given dates.

    Emitted will be the first day of each month.

    >>> list(iterate_months(datetime.date(1999, 11, 1),
    ...                     datetime.date(2000, 2, 1)))
    [datetime.date(1999, 11, 1), datetime.date(1999, 12, 1),\
 datetime.date(2000, 1, 1), datetime.date(2000, 2, 1)]

    """
    assert isinstance(start_date, datetime.date)
    assert isinstance(end_date, datetime.date)
    assert start_date < end_date

    year = start_date.year
    month = start_date.month
    while True:
        current = datetime.date(year, month, 1)
        yield current
        if current.month == end_date.month and current.year == end_date.year:
            break
        else:
            month = ((month + 1) % 12) or 12
            if month == 1:
                year += 1


if __name__ == '__main__':
    import doctest
    doctest.testmod()

To format your dates, use something like this

def format_month(date):
    return date.strftime(r"%b-%y")

Putting it all together

start = datify("2014-10-10")
end = datify("2016-01-07")

for entry in iterate_months(start, end):
    print format_month(entry)

Or save it as a list:

result = list(iterate_months(start, end))