Handle special cases for timezone identification

src/icalendar/cal.py

@@ -1392,7 +1392,6 @@ def get_used_tzids(self) -> set[str]:
         """
         result = set()
         for name, value in self.property_items(sorted=False):
-            print(name, value)
             if hasattr(value, "params"):
                 result.add(value.params.get("TZID"))
         return result - {None}

src/icalendar/tests/test_issue_722_generate_vtimezone.py

@@ -11,10 +11,10 @@
 
 from datetime import date, datetime, timedelta
 from re import findall
-from zoneinfo import available_timezones
 
 import pytest
 from dateutil.tz import gettz
+from zoneinfo import available_timezones
 
 from icalendar import Calendar, Component, Event, Timezone
 from icalendar.timezone import tzid_from_tzinfo, tzids_from_tzinfo
@@ -327,7 +327,7 @@ def test_dateutil_timezone_is_not_found_with_tzname(calendars, no_pytz):
     assert "dateutil" in repr(cal.events[0].start.tzinfo.__class__)
 
 
-@pytest.mark.parametrize("tzname", ["America/New_York", "Europe/Berlin"])
+@pytest.mark.parametrize("tzname", ["America/New_York", "Arctic/Longyearbyen"])
 # @pytest.mark.parametrize("component", ["STANDARD", "DAYLIGHT"])
 def test_dateutil_timezone_is_matched_with_tzname(tzname):
     """dateutil is an example of a timezone that has no tzid.
@@ -338,6 +338,7 @@ def test_dateutil_timezone_is_matched_with_tzname(tzname):
     cal = Calendar()
     event = Event()
     event.start = datetime(2024, 11, 12, tzinfo=gettz(tzname))
+    print(dir(event.start.tzinfo))
     cal.add_component(event)
     assert cal.get_missing_tzids() == {tzname}
     cal.add_missing_timezones()
@@ -399,7 +400,7 @@ def test_dates_before_and_after_are_considered():
     pytest.skip("todo")
 
 
-@pytest.mark.parametrize("tzid", available_timezones())
+@pytest.mark.parametrize("tzid", available_timezones() - {"Factory", "localtime"})  
 def test_we_can_identify_dateutil_timezones(tzid):
     """dateutil and others were badly supported.
 

src/icalendar/tests/test_timezone_identification.py

@@ -3,15 +3,9 @@
 import pytest
 from zoneinfo import ZoneInfo, available_timezones
 
-from icalendar.timezone import tzids_from_tzinfo
-
-tzids = available_timezones()
-try:
-    tzids.remove("Factory")
-    tzids.remove("localtime")
-except ValueError:
-    pass
+from icalendar.timezone import tzids_from_tzinfo, tzid_from_tzinfo
 
+tzids = available_timezones() - {"Factory", "localtime"}
 with_tzid = pytest.mark.parametrize("tzid", tzids)
 
 @with_tzid
@@ -30,3 +24,8 @@ def test_can_identify_dateutil(tzid):
     """Check that all those dateutil timezones can be identified."""
     from dateutil.tz import gettz
     assert tzid in tzids_from_tzinfo(gettz(tzid))
+
+def test_utc_is_identified(utc):
+    """Test UTC because it is handled in a special way."""
+    assert "UTC" in tzids_from_tzinfo(utc)
+    assert tzid_from_tzinfo(utc) == "UTC"

src/icalendar/tests/test_timezoned.py

@@ -135,15 +135,15 @@ def test_tzinfo_dateutil():
 def test_create_america_new_york(calendars, tzp):
     """testing America/New_York, the most complex example from the RFC"""
     cal = calendars.america_new_york
-    dt = cal.walk("VEVENT")[0]["DTSTART"][0].dt
+    dt = cal.events[0].start
     assert tzid_from_dt(dt) in ("custom_America/New_York", "EDT")
 
 
 def test_america_new_york_with_pytz(calendars, tzp, pytz_only):
     """Create a custom timezone with pytz and test the transition times."""
     print(tzp)
     cal = calendars.america_new_york
-    dt = cal.walk("VEVENT")[0]["DTSTART"][0].dt
+    dt = cal.events[0].start
     tz = dt.tzinfo
     tz_new_york = tzp.timezone("America/New_York")
     # for reasons (tm) the locally installed version of the timezone

src/icalendar/timezone/tzid.py

@@ -7,6 +7,7 @@
 from __future__ import annotations
 
 from typing import TYPE_CHECKING, Optional
+import dateutil.tz.tz as tz
 
 if TYPE_CHECKING:
     from datetime import datetime, tzinfo
@@ -20,16 +21,20 @@ def tzids_from_tzinfo(tzinfo: Optional[tzinfo]) -> tuple[str]:
     >>> tzids_from_tzinfo(zoneinfo.ZoneInfo("Africa/Accra"))
     ('Africa/Accra',)
     >>> from dateutil.tz import gettz
-    >>> tzids_from_tzinfo(gettz("Africa/Accra"))
-    ('Africa/Abidjan', 'Africa/Accra', 'Africa/Bamako', 'Africa/Banjul', 'Africa/Conakry', 'Africa/Dakar')
+    >>> tzids_from_tzinfo(gettz("Europe/Berlin"))
+    ('Arctic/Longyearbyen', 'Atlantic/Jan_Mayen', 'Europe/Berlin', 'Europe/Budapest', 'Europe/Copenhagen', 'Europe/Oslo', 'Europe/Stockholm', 'Europe/Vienna')
 
-    """
+    """ # The example might need to change if you recreate the lookup tree
     if tzinfo is None:
         return ()
     if hasattr(tzinfo, 'zone'):
         return (tzinfo.zone,)  # pytz implementation
     if hasattr(tzinfo, 'key'):
-        return (tzinfo.key,)  # dateutil implementation, tzinfo.key  # ZoneInfo implementation
+        return (tzinfo.key,)  # ZoneInfo implementation
+    if isinstance(tzinfo, tz._tzicalvtz):
+        return (tzinfo._tzid,)
+    if isinstance(tzinfo, tz.tzstr):
+        return (tzinfo._s,)
     return tuple(sorted(tzinfo2tzids(tzinfo)))
 
 
@@ -39,8 +44,12 @@ def tzid_from_tzinfo(tzinfo: Optional[tzinfo]) -> Optional[str]:
     Some timezones are equivalent.
     Thus, we might return one ID that is equivelant to others.
     """
-    return (tzids_from_tzinfo(tzinfo) + (None,))[0]
-
+    tzids = tzids_from_tzinfo(tzinfo)
+    if "UTC" in tzids:
+        return "UTC"
+    if not tzids:
+        return None
+    return tzids[0]
 
 def tzid_from_dt(dt: datetime) -> Optional[str]:
     """Retrieve the timezone id from the datetime object."""
@@ -67,10 +76,11 @@ def tzinfo2tzids(tzinfo: Optional[tzinfo]) -> set[str]:
     is equivalent to many others.
 
     >>> import zoneinfo
-    >>> from icalendar.timezone.equivalent_timezone_ids import tzinfo2tzids
-    >>> tzinfo2tzids(zoneinfo.ZoneInfo("Africa/Accra"))
-    ('Africa/Abidjan', 'Africa/Accra', 'Africa/Bamako', 'Africa/Banjul', 'Africa/Conakry', 'Africa/Dakar')
-    """
+    >>> from icalendar.timezone.tzid import tzinfo2tzids
+    >>> "Europe/Berlin" in tzinfo2tzids(zoneinfo.ZoneInfo("Europe/Berlin"))
+    True
+
+    """ # The example might need to change if you recreate the lookup tree
     if tzinfo is None:
         return set()
     from icalendar.timezone.equivalent_timezone_ids_result import lookup

src/icalendar/timezone/zoneinfo.py

@@ -1,21 +1,25 @@
 """Use zoneinfo timezones"""
 from __future__ import annotations
+
 try:
     import zoneinfo
-except:
-    from backports import zoneinfo
-from icalendar import prop
-from dateutil.rrule import rrule, rruleset
+except ImportError:
+    from backports import zoneinfo  # type: ignore  # noqa: PGH003
+import copy
+import copyreg
+import functools
 from datetime import datetime, tzinfo
-from typing import Optional
-from .provider import TZProvider
-from .. import cal
 from io import StringIO
+from typing import TYPE_CHECKING, Optional
+
+from dateutil.rrule import rrule, rruleset
 from dateutil.tz import tzical
 from dateutil.tz.tz import _tzicalvtz
-import copyreg
-import functools
-import copy
+
+from .provider import TZProvider
+
+if TYPE_CHECKING:
+    from icalendar import cal, prop
 
 
 class ZONEINFO(TZProvider):