How do I find the nth day of the next month in Python?

Question

I am trying to get the date delta by subtracting today's date from the nth day of the next month.

delta = nth_of_next_month - todays_date
print delta.days

How do you get the date object for the 1st (or 2nd, 3rd.. nth) day of the next month. I tried taking the month number from the date object and increasing it by 1. Which is obviously a dumb idea because 12 + 1 = 13. I also tried adding one month to today and tried to get to the first of the month. I am sure that there is a much more efficient way of doing this.

I'd imagine all you need to do is increment the month property of the date object. This previous answer shows how since the month property is not writable http://stackoverflow.com/a/4131114/333082 — cecilphillip, Jan 15 '14 at 18:45
Why do you care about "more efficient" here? The obvious and simple implementation in sunshine's answer takes only 0.46us to do all that "expensive" work, compared to 1.64us to call `now()`. So I highly doubt it will be a bottleneck in your code. The simplest implementation—one that you understand, and can debug easily—is better than the fastest one, unless it's affecting your total runtime. — abarnert, Jan 15 '14 at 19:00
@abarnert exactly what I meant... Efficient to me. Not computing power. — Johnston, Jan 15 '14 at 19:05

Jon Clements · Accepted Answer · 2014-01-15T18:55:22.017

7

The dateutil library is useful for this:

from dateutil.relativedelta import relativedelta
from datetime import datetime

# Where day is the day you want in the following month
dt = datetime.now() + relativedelta(months=1, day=20)

edited Jan 15 '14 at 18:55

answered Jan 15 '14 at 18:45

Jon Clements

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1

http://labix.org/python-dateutil#head-6a1472b7c74e5b8bab7784f11214250d34e09aa5 explains what is going on with relativedelta – Peter Lustig Jan 15 '14 at 18:52

senshin · Answer 2 · 2014-01-15T19:01:25.687

This should be straightforward unless I'm missing something in your question:

import datetime

now = datetime.datetime.now()
nth_day = 5
next_month = now.month + 1 if now.month < 12 else 1 # February
year = now.year if now.month < 12 else now.year+1
nth_of_next_month = datetime.datetime(year, next_month, nth_day)
print(nth_of_next_month)

Result:

2014-02-05 00:00:00

Using dateutil as suggested in another answer is a much better idea than this, though.

score 2 · Answer 3 · answered Jan 15 '14 at 18:51

Another alternative is to use delorean library:

Delorean is a library that provides easy and convenient datetime conversions in Python.

>>> from delorean import Delorean
>>> d = Delorean()
>>> d.next_month()
Delorean(datetime=2014-02-15 18:51:14.325350+00:00, timezone=UTC)
>>> d.next_month().next_day(2)
Delorean(datetime=2014-02-17 18:51:14.325350+00:00, timezone=UTC)

score 1 · Answer 4 · answered Jan 15 '14 at 19:19

My approach to calculating the next month without external libraries:

def nth_day_of_next_month(dt, n):
    return dt.replace(
        year=dt.year + (dt.month // 12),  # +1 for december, +0 otherwise
        month=(dt.month % 12) + 1,        # december becomes january
        day=n)

This works for both datetime.datetime() and datetime.date() objects.

Demo:

>>> import datetime
>>> def nth_day_of_next_month(dt, n):
...     return dt.replace(year=dt.year + (dt.month // 12), month=(dt.month % 12) + 1, day=n)
... 
>>> nth_day_of_next_month(datetime.datetime.now(), 4)
datetime.datetime(2014, 2, 4, 19, 20, 51, 177860)
>>> nth_day_of_next_month(datetime.date.today(), 18)
datetime.date(2014, 2, 18)

score 0 · Answer 5 · answered Jan 16 '14 at 04:35

Without using any external library, this can be achived as follows

from datetime import datetime, timedelta

def nth_day_of_next_month(n):
    today = datetime.now()
    next_month_dt = today + timedelta(days=32-today.day)
    return next_month_dt.replace(day=n)

How do I find the nth day of the next month in Python?

5 Answers5