CODEWITHSUNDEEP
pythonpython-dateutilrelativedelta
Tanzaho
Tanzaho

Reputation: 1372

Why does relativedelta with positive arguments return a date in the past?

I have some trouble to understand the behavior of dateutil.relativedelta. I understand that relativedelta could return past dates if I use negative arguments as specified in relativedelta doc.

However, when I provide positive parameters, I expect that it always return a date in the future... that seems legit right?

My use case is the following : we are Tuesday, it is 8:35. I want to get the date of the closest Monday and Tuesday at 6:00.

Here what I did. The first result seems correct to me, while the second one is wrong.

>>> import datetime
>>> now = datetime.datetime.now()
>>> now
datetime.datetime(2016, 11, 29, 8, 35, 23, 786349)

>>> from dateutil import relativedelta
>>> now.weekday()
1

>>> now + relativedelta.relativedelta(weekday=0, hour=6, minute=0) # should give a time in the future
datetime.datetime(2016, 12, 5, 6, 0, 23, 786349)  # here this is correct, in the future

>>> now + relativedelta.relativedelta(weekday=1, hour=6, minute=0) # should give a time in the future
datetime.datetime(2016, 11, 29, 6, 0, 23, 786349)  # but this is in the past / I would expect result (2016, 12, 6, 6, 0, 23, 786349)

So , am I doing something wrong here ?

Upvotes: 1

Views: 1072

Answers (2)

Twidi
Twidi

Reputation: 36

I think it's in the doc:

Starting with, about weekday:

These instances may receive a parameter N, specifying the Nth weekday, which could be positive or negative (like MO(+1) or MO(-2). Not specifying it is the same as specifying +1.

So by passing 1, it's like you're passing (1, 1)

Then, continuing on the doc, on the 7th dot of behavior of operations with relativedelta:

Notice that if the calculated date is already Monday, for example, using (0, 1) or (0, -1) won’t change the day.

So the 29th of November is already a Tuesday, and you're asking for a Tuesday.

So nothing changes.

Upvotes: 2

Bryan
Bryan

Reputation: 6752

So according to your initial date, you're actually at 8AM, but you're targeting 6AM by using the hour param, if you're trying to increment one hour, you should use hours and minutes respectively

>>> now
datetime.datetime(2016, 11, 29, 3, 5, 41, 763818)

>>> now.weekday()
1

>>> now + relativedelta.relativedelta(weekday=1, hour=1)
datetime.datetime(2016, 11, 29, 1, 5, 41, 763818) # Notice how it's in the past

>>> now + relativedelta.relativedelta(weekday=1, hours=1)
datetime.datetime(2016, 11, 29, 4, 5, 41, 763818) # Notice how it's one hour in the future

>>> n + relativedelta.relativedelta(weekday=1, hour=6, minute=0, weeks=1)
datetime.datetime(2016, 12, 6, 6, 0, 41, 763818)

Upvotes: 3

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