Tested with dateutil timezones

src/icalendar/timezone/dateutil.py

@@ -0,0 +1,69 @@
+"""Use dateutil timezones."""
+from __future__ import annotations
+import dateutil
+import dateutil.tz
+from .. import cal
+from datetime import datetime, tzinfo
+from typing import Optional
+from .provider import TZProvider
+from icalendar import prop
+from dateutil.rrule import rrule
+
+
+
+class DATEUTIL(TZProvider):
+    """Provide icalendar with timezones from dateutil."""
+
+    name = "dateutil"
+
+    def localize_utc(self, dt: datetime) -> datetime:
+        """Return the datetime in UTC."""
+        if getattr(dt, 'tzinfo', False) and dt.tzinfo is not None:
+            return dt.astimezone(dateutil.tz.tzutc())
+        # assume UTC for naive datetime instances
+        dt = dt.replace(tzinfo=dateutil.tz.tzutc())
+        return dt
+
+    def localize(self, dt: datetime, tz: tzinfo) -> datetime:
+        """Localize a datetime to a timezone."""
+        return dt.replace(tzinfo=tz)
+
+    def knows_timezone_id(self, id: str) -> bool:
+        """Whether the timezone is already cached by the implementation."""
+        return dateutil.tz.gettz(id) is not None
+
+    def fix_rrule_until(self, rrule:rrule, ical_rrule:prop.vRecur) -> None:
+        """Make sure the until value works for the rrule generated from the ical_rrule."""
+        if not {'UNTIL', 'COUNT'}.intersection(ical_rrule.keys()):
+            # dateutil.timezones don't know any transition dates after 2038
+            # either
+            rrule._until = datetime(2038, 12, 31, tzinfo=dateutil.tz.UTC)
+
+    def create_timezone(self, tz: cal.Timezone) -> tzinfo:
+        """Create a dateutil timezone from the given information."""
+        transition_times, transition_info = tz.get_transitions()
+        name = tz.tz_name
+        cls = type(name, (DstTzInfo,), {
+            'zone': name,
+            '_utc_transition_times': transition_times,
+            '_transition_info': transition_info
+        })
+        return cls
+
+    def timezone(self, name: str) -> Optional[tzinfo]:
+        """Return a timezone with a name or None if we cannot find it."""
+        try:
+            return dateutil.timezone(name)
+        except dateutil.UnknownTimeZoneError:
+            pass
+
+    def uses_dateutil(self) -> bool:
+        """Whether we use dateutil."""
+        return True
+
+    def uses_zoneinfo(self) -> bool:
+        """Whether we use zoneinfo."""
+        return False
+
+
+__all__ = ["dateutil"]