UTC time is incorrectly displayed as local time-CodePudding

I've found that some dates (at the moment I only found this error with some before-epoch dates) add an hour of difference from UTC.

Local time is GMT-3

First time I see it was in Javascript

> new Date("1969-07-26T03:00:00 00:00")
< Fri Jul 25 1969 23:00:00 GMT-0400 (-03) // why is it -0400?

> new Date("1963-07-26T03:00:00 00:00")
< Fri Jul 26 1963 00:00:00 GMT-0300 (-02)

Then I tried in Ruby and the same happened

irb(main):288:0> Time.parse("1969-07-26T03:00:00 00:00").localtime
=> 1969-07-25 23:00:00 -0400

But (maybe I did it wrong) doesn't happen in Python

In [12]: utc = datetime.fromisoformat("1969-07-26T03:00:00 00:00")

In [13]: utc.replace(tzinfo=tz.tzutc())
Out[13]: datetime.datetime(1969, 7, 26, 3, 0, tzinfo=tzutc())

In [14]: utc.astimezone(tz.tzlocal())
Out[14]: datetime.datetime(1969, 7, 26, 0, 0, tzinfo=tzlocal())

I haven't been able to find information about it. Anything to read about and how to handle those cases? For example 1963-07-26T03:00:00 00:00 works as expected.

Cheers!

CodePudding user response：

Adding 00:00 to the end of your date string is creating a UTC offset. Since you're specifying zero hours, zero minutes, and zero seconds, it's creating a zero-offset from GMT, or in other-words, setting your timezone to exactly GMT.

For example, I'm in a GMT -5 timezone (US Central). When I create a new JS date using today's date at 6am, I get a subtraction of 5 hours (because GMT -5 is my timezone) :

> new Date("2022-06-08T06:00:00 00:00")
// Wed Jun 08 2022 01:00:00 GMT-0500 (Central Daylight Time)

However, if I omit the offset, then it works as expected, and I get the date in my local timezone.

> new Date("2022-06-08T06:00:00")
// Wed Jun 08 2022 06:00:00 GMT-0500 (Central Daylight Time)

I can also run your code examples and get the expected result.

> new Date("1969-07-26T03:00:00")
// Sat Jul 26 1969 03:00:00 GMT-0500 (Central Daylight Time)

See the section