Get the named timezone for a given location in python using native macOS CoreLocation APIs

tzname.py

"""Get named timezone for a location on macOS using CoreLocation

To use this script, you need to have pyobjc-core and pyobjc-framework-CoreLocation installed:

    pip install pyobjc-core pyobjc-framework-CoreLocation

This script uses CoreLocation to get the timezone for a given latitude and longitude
as well as the timezone offset for a given date.

It effectively does the same thing as python packages like [tzfpy](https://pypi.org/project/tzfpy/)
or [timezonefinder](https://pypi.org/project/timezonefinder/) but uses macOS native APIs.

"""

# /// script
# dependencies = [
#     "pyobjc-core",
#     "pyobjc-framework-CoreLocation"
# ]
# ///

import datetime

import objc
from CoreLocation import CLGeocoder, CLLocation
from Foundation import NSDate, NSRunLoop, NSTimeZone

WAIT_FOR_COMPLETION = 0.01  # wait time for async completion in seconds
COMPLETION_TIMEOUT = 5.0  # timeout for async completion in seconds


def timezone_for_location(latitude: float, longitude: float) -> NSTimeZone:
    with objc.autorelease_pool():
        location = CLLocation.alloc().initWithLatitude_longitude_(latitude, longitude)
        geocoder = CLGeocoder.alloc().init()

        result = {"timezone": None, "error": None}
        completed = False

        def completion(placemarks, error):
            nonlocal completed
            if error:
                result["error"] = error.localizedDescription()
            else:
                placemark = placemarks[0] if placemarks else None
                if placemark and placemark.timeZone():
                    result["timezone"] = placemark.timeZone()
                else:
                    result["error"] = "Unable to determine timezone"
            completed = True

        geocoder.reverseGeocodeLocation_completionHandler_(location, completion)

        # reverseGeocodeLocation_completionHandler_ is async so run the event loop until completion
        # I usuall use threading.Event for this type of thing in pyobjc but the the thread blocked forever
        waiting = 0
        while not completed:
            NSRunLoop.currentRunLoop().runMode_beforeDate_(
                "NSDefaultRunLoopMode",
                NSDate.dateWithTimeIntervalSinceNow_(WAIT_FOR_COMPLETION),
            )
            waiting += WAIT_FOR_COMPLETION
            if waiting >= COMPLETION_TIMEOUT:
                raise TimeoutError(
                    f"Timeout waiting for completion of reverseGeocodeLocation_completionHandler_: {waiting} seconds"
                )

        if result["error"]:
            raise Exception(f"Error: {result['error']}")

        return result["timezone"]


if __name__ == "__main__":
    import argparse
    import time

    def parse_date(date_str):
        try:
            return datetime.datetime.strptime(date_str, "%Y-%m-%d %H:%M:%S")
        except ValueError:
            return datetime.datetime.strptime(date_str, "%Y-%m-%d")

    parser = argparse.ArgumentParser(description="Get timezone for a location")
    parser.add_argument("latitude", type=float, help="Latitude of location")
    parser.add_argument("longitude", type=float, help="Longitude of location")
    parser.add_argument(
        "--date",
        type=lambda d: parse_date(d),
        default=datetime.datetime.now(),
        help="Date/time for timezone offset in format 'YYYY-MM-DD HH:MM:SS' or 'YYYY-MM-DD'",
    )
    args = parser.parse_args()

    try:
        start_t = time.time_ns()
        timezone = timezone_for_location(args.latitude, args.longitude)
        offset = timezone.secondsFromGMTForDate_(
            args.date
        )  # takes an NSDate but pybojc will convert
        end_t = time.time_ns()
        print(
            f"Timezone: {timezone.name()}, offset: {offset}, took: {(end_t - start_t) / 1e6:.2f} ms"
        )
    except Exception as e:
        print(f"Error: {e}")

MIT License

Run like this:

uv run "https://gist.githubusercontent.com/RhetTbull/db70c113efd03029c6ff619f4699ce34/raw/06f34e6d64f054faa88c1caea4a4fa3968e14848/tzname.py" 34 -118

Which ouputs:

Timezone: America/Los_Angeles, offset: -28800, took: 317.20 ms

Or

uv run "https://gist.githubusercontent.com/RhetTbull/db70c113efd03029c6ff619f4699ce34/raw/06f34e6d64f054faa88c1caea4a4fa3968e14848/tzname.py" 34 -118 --date "2024-06-01"

which outputs

Timezone: America/Los_Angeles, offset: -25200, took: 264.47 ms

Thanks to @simonw for the tip on including uv script block.

Amazing. Offset accounts for DST based on sample date.

Tries to extract DST status via timezone.isDaylightSavingTime() but it comes as False in both cases. Sorry don't master Apple Foundation framework.

$ python tzname.py 43 -9 --date  "2024-06-01 10:00:00"
Timezone: Europe/Madrid, offset: 7200, took: 254.66 ms

$ python tzname.py  43 -9 --date  "2024-01-01 10:00:00" 
Timezone: Europe/Madrid, offset: 3600, took: 304.73 ms

Added:

        # Get DST information
        is_dst = timezone.isDaylightSavingTimeForDate_(args.date)
        dst_offset = timezone.daylightSavingTimeOffsetForDate_(args.date)
        dst_timezone_name = timezone.abbreviationForDate_(args.date)
        
        print(
            f"Timezone: {timezone.name()}, offset: {offset}, "
            f"DST: {is_dst}, DST offset: {dst_offset}, "
            f"DST timezone name: {dst_timezone_name}, "
            f"took: {(end_t - start_t) / 1e6:.2f} ms"
        )   

Weird. timezone.isDaylightSavingTimeForDate_(args.date) works correctly for me.

❯ python tz.py 34 -118 --date "2021-06-01"
Timezone: America/Los_Angeles, offset: -25200, DST: True, took: 281.25 ms
❯ python tz.py 34 -118 --date "2021-01-01"
Timezone: America/Los_Angeles, offset: -28800, DST: False, took: 292.69 ms

I added:

        is_dst = timezone.isDaylightSavingTimeForDate_(args.date)
        print(
            f"Timezone: {timezone.name()}, offset: {offset}, DST: {is_dst}, took: {(end_t - start_t) / 1e6:.2f} ms"
        )

Very nice, thank you