Get Timezone from City in Python/Django

Question

Using pytz, I am able to get a list of timezones like so:

>>> from pytz import country_timezones
>>> print(' '.join(country_timezones('ch')))
Europe/Zurich
>>> print(' '.join(country_timezones('CH')))
Europe/Zurich

Given that I am getting both Country and City fields from the user, how can I go about determining the timezone for the city?

Answer 1

pytz is a wrapper around IANA Time Zone Database (Olson database). It does not contain data to map an arbitrary city in the world to the timezone it is in.

You might need a geocoder such as geopy that can translate a place (e.g., a city name) to its coordinates (latitude, longitude) using various web-services:

from geopy import geocoders # pip install geopy

g = geocoders.GoogleV3()
place, (lat, lng) = g.geocode('Singapore')
# -> (u'Singapore', (1.352083, 103.819836))

Given city's latitude, longitude, it is possible to find its timezone using tz_world, an efele.net/tz map / a shapefile of the TZ timezones of the world e.g., via postgis timezone db or pytzwhere:

import tzwhere

w = tzwhere()
print w.tzNameAt(1.352083, 103.819836)
# -> Asia/Singapore

There are also web-services that allow to convert (latitude, longitude) into a timezone e.g., askgeo, geonames, see Timezone lookup from latitude longitude.

As @dashesy pointed out in the comment, geopy also can find timezone (since 1.2):

timezone = g.timezone((lat, lng)) # return pytz timezone object
# -> <DstTzInfo 'Asia/Singapore' LMT+6:55:00 STD>

GeoNames also provides offline data that allows to get city's timezone directly from its name e.g.:

#!/usr/bin/env python
import os
from collections import defaultdict
from datetime import datetime
from urllib   import urlretrieve
from urlparse import urljoin
from zipfile  import ZipFile

import pytz # pip install pytz

geonames_url = 'http://download.geonames.org/export/dump/'
basename = 'cities15000' # all cities with a population > 15000 or capitals
filename = basename + '.zip'

# get file
if not os.path.exists(filename):
    urlretrieve(urljoin(geonames_url, filename), filename)

# parse it
city2tz = defaultdict(set)
with ZipFile(filename) as zf, zf.open(basename + '.txt') as file:
    for line in file:
        fields = line.split(b'\t')
        if fields: # geoname table http://download.geonames.org/export/dump/
            name, asciiname, alternatenames = fields[1:4]
            timezone = fields[-2].decode('utf-8').strip()
            if timezone:
                for city in [name, asciiname] + alternatenames.split(b','):
                    city = city.decode('utf-8').strip()
                    if city:
                        city2tz[city].add(timezone)

print("Number of available city names (with aliases): %d" % len(city2tz))

#
n = sum((len(timezones) > 1) for city, timezones in city2tz.iteritems())
print("")
print("Find number of ambigious city names\n "
      "(that have more than one associated timezone): %d" % n)

#
fmt = '%Y-%m-%d %H:%M:%S %Z%z'
city = "Zurich"
for tzname in city2tz[city]:
    now = datetime.now(pytz.timezone(tzname))
    print("")
    print("%s is in %s timezone" % (city, tzname))
    print("Current time in %s is %s" % (city, now.strftime(fmt)))

Output

Number of available city names (with aliases): 112682

Find number of ambigious city names
 (that have more than one associated timezone): 2318

Zurich is in Europe/Zurich timezone
Current time in Zurich is 2013-05-13 11:36:33 CEST+0200

Answer 2

there have been a lot of possible solutions proposed here and they're all a bit tedious to set up.

To make things quicker for the next person with this problem, I took the one from Will Charlton and made a quick python library out of it: https://pypi.python.org/pypi/whenareyou

from whenareyou import whenareyou
tz = whenareyou('Hamburg')
tz.localize(datetime(2002, 10, 27, 6, 0, 0))

Gets you datetime.datetime(2002, 10, 27, 6, 0, tzinfo=<DstTzInfo 'Europe/Berlin' CET+1:00:00 STD>) .

This gets you a pytz object (tz in the example) so you can use it pythonicly.

• It uses the google API
• Leaves daylight savings calculation to pytz, only one call per city, rest happens offline
• LRU caches the requests so you shouldn't hit the API limit easily
• Should also work with any address or anything google maps understands

Answer 3

I think you're going to need to manually search the timezone database for the city you're looking for:

from pytz import country_timezones, timezone

def find_city(query):
    for country, cities in country_timezones.items():
        for city in cities:
            if query in city:
                yield timezone(city)

for tz in find_city('Zurich'):
    print(tz)

(that's just a quick-and-dirty solution, it for instance doesn't try to match only the city-part of a timezone – try searching for Europe, it does substring matches, doesn't search case-insensitive, etc.)