[Bug 1995452] Re: Invalid daylight saving time info for 'Europe/Dublin'

[Benjamin Drung]

Thank you for taking the time to report this bug and helping to make
Ubuntu better.

I rewrote your snippet with Python's zoneinfo (from Python >= 3.9):

```
import zoneinfo
from datetime import datetime, timedelta

def is_dst(zonename):
    tz = zoneinfo.ZoneInfo(zonename)
    now = datetime.now(tz=tz)
    return now.dst() != timedelta(0)

is_dst('Europe/Dublin')
```

I verified that both code snippets work for Europe/Berlin. Then I looked
into tzdata and found the reason in `europe`:

# From Paul Eggert (2017-12-07):
# The 1996 anonymous contributor's goal was to determine the correct
# abbreviation for summer time in Dublin and so the contributor
# focused on the "IST", not on the "Irish Summer Time".  Though the
# "IST" was correct, the "Irish Summer Time" appears to have been an
# error, as Ireland's Standard Time (Amendment) Act, 1971 states that
# standard time in Ireland remains at UT +01 and is observed in
# summer, and that Greenwich mean time is observed in winter.  (Thanks
# to Derick Rethans for pointing out the error.)  That is, when
# Ireland amended the 1968 act that established UT +01 as Irish
# Standard Time, it left standard time unchanged and established GMT
# as a negative daylight saving time in winter.  So, in this database
# IST stands for Irish Summer Time for timestamps before 1968, and for
# Irish Standard Time after that.  See:
# http://www.irishstatutebook.ie/eli/1971/act/17/enacted/en/print

So python-tz works correctly. If you want Europe/Dublin changed, please
contact upstream tzdata (see https://www.iana.org/time-zones).

** Description changed:

  I'm trying to check if daylight saving time is in effect for the
  'Europe/Dublin'. Executing the following line:
  
  datetime.datetime.now(pytz.timezone('Europe/Dublin')).dst()
  
  is giving 0 as a result, which is incorrect because during the day that
  I was executing the command (2022/10/17) was still daylight saving time
  in effect so the function should return a dst offset value.
  
  The function below also returned the wrong result (False instead of
  True) for the date 2022/10/17:
  
+ ```
  import pytz
  from datetime import datetime, timedelta
  
  def is_dst(zonename):
-     tz = pytz.timezone(zonename)
-     now = pytz.utc.localize(datetime.utcnow())
-     return now.astimezone(tz).dst() != timedelta(0)
+     tz = pytz.timezone(zonename)
+     now = pytz.utc.localize(datetime.utcnow())
+     return now.astimezone(tz).dst() != timedelta(0)
  
  is_dst('Europe/Dublin')
+ ```

** Changed in: python-tz (Ubuntu)
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1995452

Title:
  Invalid daylight saving time info for 'Europe/Dublin'

Status in python-tz package in Ubuntu:
  Invalid

Bug description:
  I'm trying to check if daylight saving time is in effect for the
  'Europe/Dublin'. Executing the following line:

  datetime.datetime.now(pytz.timezone('Europe/Dublin')).dst()

  is giving 0 as a result, which is incorrect because during the day
  that I was executing the command (2022/10/17) was still daylight
  saving time in effect so the function should return a dst offset
  value.

  The function below also returned the wrong result (False instead of
  True) for the date 2022/10/17:

  ```
  import pytz
  from datetime import datetime, timedelta

  def is_dst(zonename):
      tz = pytz.timezone(zonename)
      now = pytz.utc.localize(datetime.utcnow())
      return now.astimezone(tz).dst() != timedelta(0)

  is_dst('Europe/Dublin')
  ```

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