Why converting between time zones in Python yields different results?

Question

I have been working with time zones in Python for some time now. One of my challenges was creating an prize which was valid up to 23:59:59 on the proper time zone some days after the current time. I took the current UTC time, added a timedelta, converted to the desired time zone, replaced hour/minutes/seconds and converted back to UTC. That worked and still works perfectly.

Recently I tried to rewrite that code on another project and came to a situation which I cannot explain. Check out the example code below.

from datetime import datetime
import pytz

dt1 = datetime\
.now(pytz.utc)\
.astimezone(pytz.timezone("America/Sao_Paulo"))\
.replace(
    year=2018,
    month=3,
    day=22,
    hour=23,
    minute=59,
    second=59,
    microsecond=0
)\
.astimezone(pytz.utc)

dt2=datetime(
    year=2018,
    month=3,
    day=22,
    hour=23,
    minute=59,
    second=59,
    microsecond=0,
    tzinfo=pytz.timezone("America/Sao_Paulo")
)\
.astimezone(pytz.utc)

print(dt1)
# 2018-03-23 02:59:59+00:00
print(dt2)
# 2018-03-23 03:05:59+00:00

Why dt1 != dt2 ?

I know dt1 is an ugly way to create a datetime object, but that is actually the value I expect. I cannot understand why they differ in 6 minutes.

Thank you very much.

Jeremy · Accepted Answer · 2018-03-23 00:16:59Z

2

Quoting from the pytz documentation :

Unfortunately using the tzinfo argument of the standard datetime constructors ‘’does not work’’ with pytz for many timezones.

Take a look at your dt2 before converting it to UTC and you'll see there's something fishy going on with its UTC offset:

>>> dt2 = datetime(year=2018, month=3, day=22,
...                hour=23, minute=59, second=59,
...                tzinfo=pytz.timezone("America/Sao_Paulo"))
>>> print(dt2)
2018-03-22 23:59:59-03:06

This on the other hand works:

>>> naive_dt = datetime(year=2018, month=3, day=22,
...                     hour=23, minute=59, second=59)
>>> aware_dt = pytz.timezone('America/Sao_Paulo').localize(naive_dt)
>>> print(aware_dt)
2018-03-22 23:59:59-03:00

edited Mar 23, 2018 at 0:16

answered Mar 23, 2018 at 0:11

Jeremy

1,39811 silver badges12 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Heits Over a year ago

I could not find any of that on the docs I searched. That is actually a bug on the datetime constructors with time zones. Thank you very much for pointing it out!

Matt Johnson-Pint Over a year ago

Not trying to be rude or anything, but I'm curious why you couldn't find this in the docs when it's in the note immediately after the package description at the very top of the introduction section, and then shows examples about 1 paragraph down from there. Is there some other way the docs could highlight this better for you?

Collectives™ on Stack Overflow

Why converting between time zones in Python yields different results?

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related