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I have a year value and a day of year and would like to convert to a date (day/month/year).

martineau
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Mino
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6 Answers6

117
datetime.datetime(year, 1, 1) + datetime.timedelta(days - 1)
Ignacio Vazquez-Abrams
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    How is this simpler than SilentGhost's answer? – GreenMatt Sep 27 '12 at 16:43
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    @GreenMatt: It doesn't involve putting the numbers into a string and then parsing that string. – Ignacio Vazquez-Abrams Sep 27 '12 at 16:46
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    This was really meant for Mino; I guess I should have put "@Mino" in the comment, sorry. It's true that this method does not require converting numbers to a string; however, in my experience you're at least equally likely to be starting with a string. More to the point, two calls and an arithematic operation are more complicated than a single call IMO. (Granted, the number of calls will depend on any conversions needed.) – GreenMatt Sep 27 '12 at 20:18
  • I upvoted this answer because it also works for decimal days. I submitted an edit to add that. – Jeff Ellen May 11 '18 at 22:33
34
>>> import datetime
>>> datetime.datetime.strptime('2010 120', '%Y %j')
datetime.datetime(2010, 4, 30, 0, 0)
>>> _.strftime('%d/%m/%Y')
'30/04/2010'
SilentGhost
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8

The toordinal() and fromordinal() functions of the date class could be used:

from datetime import date
date.fromordinal(date(year, 1, 1).toordinal() + days - 1)
sth
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6

since it is pretty common these days, a pandas option, using pd.to_datetime with specified unit and origin:

import pandas as pd

day, year = 21, 2021

print(pd.to_datetime(day-1, unit='D', origin=str(year)))
# 2021-01-21 00:00:00
FObersteiner
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  • When day and year are already in a dataframe, then... `df['md'] = pd.to_datetime(df['day'], format='%j').dt.strftime('%m-%d')`. And `df['dt'] = pd.to_datetime(df['year'].astype(str) + '-' + df.md)`. – There May 14 '23 at 21:11
0

Using the mx.DateTime module to get the date is similar to what has been proposed above using datetime and timedelta. Namely:

import mx.DateTime as dt 
date = dt.DateTime(yyyy,mm,dd) + dt.DateTimeDeltaFromDays(doy-1)

So, given that you know the year (say, 2020) and the doy (day of the year, say 234), then:

date = dt.DateTime(2020,1,1) + dt.DateTimeFromDays(233)

which returns

2020-08-21 00:00:00.00

The advantage of the mx.DateTime library is that has many useful features. As per description in its homepage:

  • Parses date/time string values in an almost seamless way.
  • Provides conversion routines to and from many different alternative date/time storage formats.
  • Includes an easy-to-use C API which makes integration a breeze.
  • Fast, memory efficient, accurate.
  • Georgian and Julian calendar support.
  • Vast range of valid dates (including B.C. dates).
  • Stable, robust and portable (mxDateTime has been around for almost 15 years now).
  • Fully interoperates with Python's time and datetime modules.
Use Me
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-1
>>>import datetime
>>>year = int(input())
>>>month = int(input())
>>>day = int(input())
data = datetime.datetime(year,month,day)
daynew = data.toordinal()
yearstart = datetime.datetime(year,1,1)
day_yearstart = yearstart.toordinal()
print ((daynew-day_yearstart)+1)
Egor014
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