Group a datetime-range over months

group_by_months.py

from datetime import datetime, timedelta

def group_by_months(since, until):
    """Group a datetime range into month-based ranges with breaks at midnight.

    >>> a = datetime(2015,11,5,3,12,5)
    >>> b = datetime(2016,3,7,4,32,10)
    >>> for i, (since, until) in enumerate(group_by_months(a, b)):
    ...     print i, 
    ...     print since.strftime('%Y.%m.%d %H:%M:%S'), 
    ...     print until.strftime('%Y.%m.%d %H:%M:%S')
    ... 
    0 2015.11.05 03:12:05 2015.11.30 23:59:59
    1 2015.12.01 00:00:00 2015.12.31 23:59:59
    2 2016.01.01 00:00:00 2016.01.31 23:59:59
    3 2016.02.01 00:00:00 2016.02.29 23:59:59
    4 2016.03.01 00:00:00 2016.03.07 04:32:10
    >>>

    Or if there's no time present, only dates

    >>> a = datetime(2015,11,5)
    >>> b = datetime(2016,3,7)
    >>> for i, (since, until) in enumerate(group_by_months(a, b)):
    ...     print i, 
    ...     print since.strftime('%Y.%m.%d %H:%M:%S'), 
    ...     print until.strftime('%Y.%m.%d %H:%M:%S')
    ... 
    0 2015.11.05 00:00:00 2015.11.30 23:59:59
    1 2015.12.01 00:00:00 2015.12.31 23:59:59
    2 2016.01.01 00:00:00 2016.01.31 23:59:59
    3 2016.02.01 00:00:00 2016.02.29 23:59:59
    4 2016.03.01 00:00:00 2016.03.07 00:00:00
    >>>
    """
    _current = since
    _month = _current.month
    while _current <= until:
        if _current == since:
            start = since
        elif _month != _current.month:
            stop = datetime(_current.year, _current.month, _current.day)
            yield start, stop - timedelta(seconds=1)
            _month = _current.month
            start = stop
        _current += timedelta(hours=24)
    yield start, until