Simplify datetime with tzinfo example

Move the example in the documentation to just use timezone.utc and a
user defined Kabul timezone rather than having two user defined
timezones with DST.

Kabul timezone is still interesting as it changes its offset but not
based on DST. This is more accurate as the previous example was missing
information about the fold attribute. Additionally, implementing the fold
attribute was rather complex and probably not relevant enough for the
section "datetime with tzinfo".

Author: mariocj89

Doc/library/datetime.rst

@@ -1316,56 +1316,35 @@ Examples of working with datetime objects:
 
 Using datetime with tzinfo:
 
-    >>> from datetime import timedelta, datetime, tzinfo
-    >>> class TZ1(tzinfo):
+    >>> from datetime import timedelta, datetime, tzinfo, timezone
+    >>> class KabulTz(tzinfo):
+    ...     # Kabul used +4 until 1045, when they moved to +4:30
     ...     def utcoffset(self, dt):
-    ...         return timedelta(hours=1) + self.dst(dt)
-    ...     def dst(self, dt):
-    ...         # DST starts last Sunday in March
-    ...         d = datetime(dt.year, 4, 1)   # ends last Sunday in October
-    ...         self.dston = d - timedelta(days=d.weekday() + 1)
-    ...         d = datetime(dt.year, 11, 1)
-    ...         self.dstoff = d - timedelta(days=d.weekday() + 1)
-    ...         if self.dston <=  dt.replace(tzinfo=None) < self.dstoff:
-    ...             return timedelta(hours=1)
+    ...         if dt.year >= 1945:
+    ...             return timedelta(hours=4, minutes=30)
     ...         else:
-    ...             return timedelta(0)
-    ...     def tzname(self,dt):
-    ...         return "UTC +2" if self.dst(dt) else "UTC +1"
-    ...
-    >>> class TZ2(tzinfo):
-    ...     def utcoffset(self, dt):
-    ...         return timedelta(hours=2) + self.dst(dt)
+    ...             return timedelta(hours=4)
     ...     def dst(self, dt):
-    ...         d = datetime(dt.year, 4, 1)
-    ...         self.dston = d - timedelta(days=d.weekday() + 1)
-    ...         d = datetime(dt.year, 11, 1)
-    ...         self.dstoff = d - timedelta(days=d.weekday() + 1)
-    ...         if self.dston <=  dt.replace(tzinfo=None) < self.dstoff:
-    ...             return timedelta(hours=1)
-    ...         else:
     ...             return timedelta(0)
     ...     def tzname(self,dt):
-    ...         return "UTC +3" if self.dst(dt) else "UTC +2"
+    ...         return "Asia/Kabul"
     ...
-    >>> tz1 = TZ1()
-    >>> # Daylight Saving Time
-    >>> dt1 = datetime(2006, 11, 21, 16, 30, tzinfo=tz1)
-    >>> dt1.dst()
-    datetime.timedelta(0)
+    ...
+    >>> tz1 =KabulTz()
+    >>> # Datetime before the change
+    >>> dt1 = datetime(1900, 11, 21, 16, 30, tzinfo=tz1)
     >>> dt1.utcoffset()
-    datetime.timedelta(seconds=3600)
+    datetime.timedelta(0, 14400)
+    >>> # Datetime after the change
     >>> dt2 = datetime(2006, 6, 14, 13, 0, tzinfo=tz1)
-    >>> dt2.dst()
-    datetime.timedelta(seconds=3600)
     >>> dt2.utcoffset()
-    datetime.timedelta(seconds=7200)
+    datetime.timedelta(0, 16200)
     >>> # Convert datetime to another time zone
-    >>> dt3 = dt2.astimezone(TZ2())
+    >>> dt3 = dt2.astimezone(timezone.utc)
     >>> dt3     # doctest: +ELLIPSIS
-    datetime.datetime(2006, 6, 14, 14, 0, tzinfo=<TZ2 object at 0x...>)
+    datetime.datetime(2006, 6, 14, 8, 30, tzinfo=datetime.timezone.utc)
     >>> dt2     # doctest: +ELLIPSIS
-    datetime.datetime(2006, 6, 14, 13, 0, tzinfo=<TZ1 object at 0x...>)
+    datetime.datetime(2006, 6, 14, 13, 0, tzinfo=<KabulTz object at 0x...>)
     >>> dt2.utctimetuple() == dt3.utctimetuple()
     True