World Timezone Image from www.physicalgeography.net
When we develop web applications some times we need multiple timezone support. If we don’t have any previous experience then it might be a tough and confusing job. Here I will help you to get some basics of Timezone conversion.
I have been used timezone with django application, but the concept is same for all languages.So here I will explain things using python timezone module "pytz". You have to install this module first into your system by using "easy_install"
Install python timezone module.
This python module support all major timezones and it helps to convert date and time in one timezone to any other timezones.You can use the human readable tiemzone names in pytz module to represent the local timezones.( like Asia/Kolkata, Europe/Paris, EST etc. ).
When we deal with multiple timezone in our application, we might have backend database where we store these date and time informations. Most databases are support UTC as it's the common timezone format. And it's better to keep a unique timezone information when saving the date and time in database and database engines not going to support all timezone formats directly. So we need to stick with commonly used UTC/GMT (Coordinated Universal Time) timezone format , it also helps to remove the daylight saving issues.
Here is the strategies used in web applications with multiple timezone support :-
- Save Date and Time information’s in database as UTC format.
- Convert the UTC time to corresponding local timezones, based on the user request and location.
Bellow I'm explaining some real scenarios where we need to change time zone information's from UTC to local and vice versa,
1. Saving Date and Time in Database :-
We always save date and time information in database as UTC standard. In django/Rails or other Framworks we have an option to set Projects default tiemzone as UTC. So in our database the time and date are always in UTC. If above methods are not working for your application you manually need to convert the local system time into UTC format and then save it. Below code sample explain things more clearly,
haridas@haridas-debian:~$ python Python 2.6.6 (r266:84292, Dec 27 2010, 00:02:40) [GCC 4.4.5] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> >>> import pytz >>> import datetime >>> local_system = datetime.datetime.now() #Get local system time and date. >>> local_system datetime.datetime(2011, 5, 7, 9, 42, 23, 751976) >>> >>> local_system_utc = datetime.datetime.utcnow() # utcnow() function give the UTC time of current local time. >>> local_system_utc # But this date tupple doesn't have the timezone information. datetime.datetime(2011, 5, 7, 5, 42, 49, 253618) #We call it as Naive representation(Date object without Timezone information.) >>> >>> local_system_utc.tzinfo #This output None value or nothing. >>> >>> >>> local_system_utc = pytz.utc.localize(local_system_utc) #Adding timezone information to "local_system_utc" >>> >>> local_system_utc datetime.datetime(2011, 5, 7, 5, 42, 49, 253618, tzinfo=<UTC>) #you can see the tzinfo variable included with the datetime tuple. #But when saving UTC time inside DB you can use naive representation of datetime object in UTC. #You can do the tzinfo addition when retrieving the time from DB.
By this way we can save time and date in Database even-though users are from different timezone. We need to consider them only when retrieving the time object from database, ie; we need to convert our UTC time to user specific timezone. So this conversion is only for view purpose.
2. Converstion from UTC to localtime
We need to convert UTC times to corresponding user timezone, follow the bellow method,
>>> import pytz >>> import datetime >>> >>> now_utc = datetime.datetime.utcnow() #Our UTC naive time from DB, for the time being here I'm taking it as current system UTC time.. >>> now_utc datetime.datetime(2011, 5, 9, 6, 36, 39, 883479) # UTC time in Naive form. >>> >>> local_tz = pytz.timezone('Europe/Paris') #Our Local timezone, to which we want to convert the UTC time. >>> >>> now_utc = pytz.utc.localize(now_utc) #Add Timezone information to UTC time. >>> >>> now_utc datetime.datetime(2011, 5, 9, 6, 36, 39, 883479, tzinfo=<UTC>) # The full datetime tuple >>> >>> local_time = now_utc.astimezone(local\_tz) # Convert to local time. >>> >>> local_time #Current local time in Paris datetime.datetime(2011, 5, 9, 8, 36, 39, 883479, tzinfo=<DstTzInfo 'Europe/Paris' CEST+2:00:00 DST>) >>>
3. Manage Browser Local Time at Server
Rather than just conversion of UTC time, some times we need to fetch records from the Database in between particular interval of local time time, for eg; From 07:00 Morning to 22:30 Evening of local time. Here our data is in UTC format, so we need to get the corresponding UTC time of these local time interval and then search the DB, you can follow bellow method,
- From browser you will get time in epoch format (A unique number to represent a particular time) or in string format ie; Y-M-D-H-M-S
- Convert this epoch time to python UTC time.
- Then search the Database.
You can reconstruct the javascrpt string format of the date in to python date object by,
>>> import datetime >>> import pytz >>> >>> datetime.datetime(year=2011,month=6,day=7,hour=10,minute=26,second=45) datetime.datetime(2011, 6, 7, 10, 26, 45) >>> local_date = datetime.datetime(year=2011,month=6,day=7,hour=10,minute=26,second=45) >>> >>> #From DB we will get the corresponding users timezone information , for eg; we can take 'America/Chicago' as our local timezone. >>> timezone = pytz.timezone('America/Chicago') >>> local_std_date = timezone.localize(local\_date,is\_dst=True) >>> >>> local_std_date datetime.datetime(2011, 6, 7, 10, 26, 45, tzinfo=<DstTzInfo 'America/Chicago' CDT-1 day, 19:00:00 DST>) >>> >>> #Now you have standard localtime and it can be easily converted to the UTC and then do the Database search and other things. >>> local_utc = local_std\_date.astimezone(pytz.utc) >>> local_utc datetime.datetime(2011, 6, 7, 15, 26, 45, tzinfo=<UTC>) >>>