datetime ISO week says first and last day of year are both in same week

user_5736515 0
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I'm running Python 3.8.3 and I found something weird about the ISO Week format (%V) :

The first day and the last day of 2019 are both in week 1.

from datetime import date
print(date(2019, 1, 1).strftime('%Y-W%V'))
print(date(2019, 12, 29).strftime('%Y-W%V'))
print(date(2019, 12, 31).strftime('%Y-W%V'))

Output:

2019-W01  
2019-W52  
2019-W01

Why does it behave like that?

python-datetime datetime-format python-3.x python
1 Answers

It is fully correct.

As you see in your dates, all of them are in 2019, so it is correct to get 2019 with %Y.

Week number is defined by ISO, and so one week could be considered in previous or in next year.

You need to use %G to get year of the week number (%V).

user_27588230
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