Elegant way to convert python datetime.timedelta to dateutil.relativedelta

Question

Is there an elegant was to convert between relativedelta and timedelta?

The use case is getting user input ISO date. Python's isodate will return either isodate.duration.Duration or datetime.timedelta.

We need the features of relativedelta (per What is the difference between "datetime.timedelta" and "dateutil.relativedelta.relativedelta" when working only with days? -- it does more) so need to convert both these types to a relativedata.

Answer 1

Just take the total number of seconds and microseconds, that's all a timedelta object stores:

def to_relativedelta(tdelta):
    return relativedelta(seconds=int(tdelta.total_seconds()),
                         microseconds=tdelta.microseconds)

>>> to_relativedelta(timedelta(seconds=0.3))
relativedelta(microseconds=+300000)
>>> to_relativedelta(timedelta(seconds=3))
relativedelta(seconds=+3)
>>> to_relativedelta(timedelta(seconds=300))
relativedelta(minutes=+5)
>>> to_relativedelta(timedelta(seconds=3000000))
relativedelta(days=+34, hours=+17, minutes=+20)

Answer 2

d = datetime.timedelta(...)
dateutil.relativedelta.relativedelta(seconds=d.total_seconds())

Answer 3

Using seconds directly with relativedelta does not populate the months and years fields and there is a reason of course that we wouldn't know if it's a leap year or a month with 31 days.

So something like this:

[In]:  tdelta = datetime.now() - datetime(1971, 1, 1)
[In]:  relativedelta(seconds=tdelta.total_seconds())
[Out]: relativedelta(days=+16958, hours=+13, minutes=+19, seconds=+49)

gives relative delta with lots of days and no months. While this can be okay in certain cases, in some we might need the years and months. Therefore:

def timedelta_to_relativedelta(tdelta):
    assert isinstance(tdelta, timedelta)

    seconds_in = {
        'year'  : 365 * 24 * 60 * 60,
        'month' : 30 * 24 * 60 * 60,
        'day'   : 24 * 60 * 60,
        'hour'  : 60 * 60,
        'minute': 60
    }

    years, rem = divmod(tdelta.total_seconds(), seconds_in['year'])
    months, rem = divmod(rem, seconds_in['month'])
    days, rem = divmod(rem, seconds_in['day'])
    hours, rem = divmod(rem, seconds_in['hour'])
    minutes, rem = divmod(rem, seconds_in['minute'])
    seconds = rem

    return relativedelta(years=years, months=months, days=days, hours=hours, minutes=minutes, seconds=seconds)

This might not be a very Pythonic solution but it works.

Note: This assumes that a year has 365 days (ignores leap non leap years) and months have 30 days.