Correctly infer timezone from event begin time (#125)

* Correctly infer timezone from event begin time

Timezones can come from the YAML file (`timezone: ...`), or from the
event start time: `2025-07-15 17:00:00 +00:00`

However it is specified, this timezone should be propagated to the
RRULE.

This PR is also a bit more strict, failing when the timezone specifier
is unrecognized.

* More strict IANA name verification

* On Windows, install timezone database

* Add additional timezone tests

* Fix tests on Windows

Author: stefanv

README.md

@@ -60,6 +60,8 @@ events:
       In this meeting we will ...
 ```
 
+Valid timezones are listed at https://datetime.app/iana-timezones
+
 ## Contributing
 
 Contributions are welcomed! This project is still in active development

pyproject.toml

@@ -27,7 +27,8 @@ dependencies = [
     "ics == 0.8.0.dev0",
     "python-dateutil >= 2.8",
     "pyyaml >= 6",
-    "importlib-resources >= 5.2.1"
+    "importlib-resources >= 5.2.1",
+    "tzdata; platform_system == 'Windows'"
 ]
 
 [project.optional-dependencies]

tests/test_cli.py

@@ -1,8 +1,11 @@
+import datetime
+import io
 import os
 
 import pytest
+import zoneinfo
 
-from yaml2ics import event_from_yaml, main
+from yaml2ics import event_from_yaml, files_to_events, main
 
 basedir = os.path.abspath(os.path.join(os.path.dirname(__file__)))
 example_calendar = os.path.join(basedir, "../example/test_calendar.yaml")
@@ -21,18 +24,28 @@ def test_cli():
 
 
 def test_errors():
+    begin = datetime.date(2025, 12, 1)
     with pytest.raises(RuntimeError) as e:
-        event_from_yaml({"repeat": {"interval": {}}})
+        event_from_yaml({"begin": begin, "repeat": {"interval": {}}})
     assert "interval must specify" in str(e)
 
     with pytest.raises(RuntimeError) as e:
-        event_from_yaml({"ics": "123"})
+        event_from_yaml({"begin": begin, "ics": "123"})
     assert "Invalid custom ICS" in str(e)
 
     with pytest.raises(RuntimeError) as e:
-        event_from_yaml({"repeat": {"interval": {"weeks": 1}}})
+        event_from_yaml({"begin": begin, "repeat": {"interval": {"weeks": 1}}})
     assert "must specify end date for repeating events" in str(e)
 
     with pytest.raises(RuntimeError) as e:
-        event_from_yaml({"repeat": {"interval": {"epochs": 4}}})
+        event_from_yaml({"begin": begin, "repeat": {"interval": {"epochs": 4}}})
     assert "expected interval to be specified in seconds, minutes" in str(e)
+
+
+def test_invalid_timezone():
+    f = io.BytesIO(b"""
+    name: Invalid tz cal
+    timezone: US/Pacificana
+     """)
+    with pytest.raises(zoneinfo.ZoneInfoNotFoundError):
+        files_to_events([f])

tests/test_events.py

@@ -1,4 +1,6 @@
-from yaml2ics import event_from_yaml
+import io
+
+from yaml2ics import event_from_yaml, files_to_events
 
 from .util import parse_yaml
 
@@ -145,3 +147,29 @@ def test_event_with_custom_ics():
     )
     event_str = event.serialize()
     assert "RRULE:FREQ=YEARLY;UNTIL=20280422T000000" in event_str
+
+
+def test_events_with_multiple_timezones():
+    f = io.BytesIO(b"""
+        name: Multiple Timezone Cal
+        timezone: America/Los_Angeles
+        events:
+          - summary: Meeting A
+            begin: 2025-07-15 17:00:00 +00:00
+            duration: { minutes: 60 }
+          - summary: Meeting B
+            timezone: UTC
+            begin: 2025-12-01 09:00:00
+            duration: { minutes: 60 }
+          - summary: Meeting C
+            begin: 2025-09-02 17:00:00
+            duration: { minutes: 60 }
+          - summary: Meeting D
+            begin: 2025-12-01 09:00:00
+            duration: { minutes: 60 }
+    """)
+    events, _ = files_to_events([f])
+    assert events[0].begin.tzname() in ("UTC", "Coordinated Universal Time")
+    assert events[1].begin.tzname() in ("UTC", "Coordinated Universal Time")
+    assert events[2].begin.tzname() == "PDT"
+    assert events[3].begin.tzname() == "PST"

yaml2ics.py

@@ -13,7 +13,8 @@
 import dateutil.rrule
 import ics
 import yaml
-from dateutil.tz import gettz
+import zoneinfo
+from dateutil.tz import gettz as _gettz
 
 interval_type = {
     "seconds": dateutil.rrule.SECONDLY,
@@ -41,6 +42,12 @@ def utcnow():
         return datetime.datetime.utcnow().replace(tzinfo=dateutil.tz.UTC)
 
 
+def gettz(tzname: str) -> datetime.tzinfo:
+    # Run this to ensure the timezone is valid IANA name
+    zoneinfo.ZoneInfo(tzname)
+    return _gettz(tzname)
+
+
 # See RFC2445, 4.8.5 REcurrence Component Properties
 # This function can be used to add a list of e.g. exception dates (EXDATE) or
 # recurrence dates (RDATE) to a reoccurring event
@@ -62,7 +69,8 @@ def event_from_yaml(event_yaml: dict, tz: datetime.tzinfo = None) -> ics.Event:
     ics_custom = d.pop("ics", None)
 
     if "timezone" in d:
-        tz = gettz(d.pop("timezone"))
+        tzname = d.pop("timezone")
+        tz = gettz(tzname)
 
     # Strip all string values, since they often end on `\n`
     for key in d:
@@ -76,6 +84,15 @@ def event_from_yaml(event_yaml: dict, tz: datetime.tzinfo = None) -> ics.Event:
     # organizer, geo, classification
     event = ics.Event(**d)
 
+    event.dtstamp = utcnow()
+    if tz and event.floating and not event.all_day:
+        event.replace_timezone(tz)
+
+    # At this point, we are sure that our event has a timezone
+    # Either it was set in the YAML file under `timezone: ...`,
+    # or it was inferred from event start time.
+    tz = event.timespan.begin_time.tzinfo
+
     # Handle all-day events
     if not ("duration" in d or "end" in d):
         event.make_all_day()
@@ -129,10 +146,6 @@ def event_from_yaml(event_yaml: dict, tz: datetime.tzinfo = None) -> ics.Event:
             rdates = [datetime_to_str(rdate) for rdate in repeat["also_on"]]
             add_recurrence_property(event, "RDATE", rdates, tz)
 
-    event.dtstamp = utcnow()
-    if tz and event.floating and not event.all_day:
-        event.replace_timezone(tz)
-
     if ics_custom:
         for line in ics_custom.split("\n"):
             if not line: