Months range

month_range.py

import itertools
import functools
from typing import Iterator

import datetime
from dateutil.relativedelta import relativedelta


def month_range(
    start: datetime.date,
    end: datetime.date,
) -> Iterator[datetime.date]:
    """Yields the 1st day of each month in the given date range."""
    yield from itertools.takewhile(
        lambda date: date < end,
        itertools.accumulate(
            itertools.repeat(relativedelta(months=1)),
            operator.add,
            initial=start,
        )
    )


if __name__ == '__main__':
    print(list(month_range(
        datetime.date(2017, 1, 1),
        datetime.date(2018, 3, 4),
    )))

# [
#     datetime.date(2017, 1, 1), datetime.date(2017, 2, 1), datetime.date(2017, 3, 1), datetime.date(2017, 4, 1),
#     datetime.date(2017, 5, 1), datetime.date(2017, 6, 1), datetime.date(2017, 7, 1), datetime.date(2017, 8, 1),
#     datetime.date(2017, 9, 1), datetime.date(2017, 10, 1), datetime.date(2017, 11, 1), datetime.date(2017, 12, 1),
#     datetime.date(2018, 1, 1), datetime.date(2018, 2, 1), datetime.date(2018, 3, 1)
# ]

I attempted to replace lambda date: date < end with functools.partial(operator.le, b=end) but operator.le does not treat b as a keyword argument. Not sure if that is possible.

P. S. This requires Python 3.8 due to initial= argument for itertools.accumulate().