How do you convert a datetime/timestamp from one timezone to another timezone?
Question:
Specifically, given the timezone of my server (system time perspective) and a timezone input, how do I calculate the system time as if it were in that new timezone (regardless of daylight savings, etc)?
import datetime
current_time = datetime.datetime.now() #system time
server_timezone = "US/Eastern"
new_timezone = "US/Pacific"
current_time_in_new_timezone = ???
Answers:
If you know your origin timezone and the new timezone that you want to convert it to, it turns out to be very straightforward:
-
Make two pytz.timezone objects, one for the current timezone and one for the new timezone e.g. pytz.timezone("US/Pacific"). You can find a list of all official timezones in pytz library: import pytz; pytz.all_timezones
-
Localize the datetime/timestamp of interest to the current timezone e.g.
current_timezone = pytz.timezone("US/Eastern")
localized_timestamp = current_timezone.localize(timestamp)
- Convert to new timezone using
.astimezone() on the newly localized datetime/timestamp from step 2 with the desired timezone’s pytz object as input e.g. localized_timestamp.astimezone(new_timezone).
Done!
As a full example:
import datetime
import pytz
# a timestamp I'd like to convert
my_timestamp = datetime.datetime.now()
# create both timezone objects
old_timezone = pytz.timezone("US/Eastern")
new_timezone = pytz.timezone("US/Pacific")
# two-step process
localized_timestamp = old_timezone.localize(my_timestamp)
new_timezone_timestamp = localized_timestamp.astimezone(new_timezone)
# or alternatively, as an one-liner
new_timezone_timestamp = old_timezone.localize(my_timestamp).astimezone(new_timezone)
Bonus: but if all you need is the current time in a specific timezone, you can conveniently pass that timezone directly into datetime.now() to get the current times directly:
datetime.datetime.now(new_timezone)
When it comes to needing timezones conversions generally, I would strongly advise that one should store all timestamps in your database in UTC, which has no daylight savings time (DST) transition. And as a good practice, one should always choose to enable time zone support (even if your users are all in a single time zone!). This will help you avoid the DST transition problem that plagues so much software today.
Beyond DST, time in software can be generally quite tricky. To get a sense of just how difficult it is to deal with time in software in general, here is a potentially enlightening resource: http://yourcalendricalfallacyis.com
Even a seemingly simple operation as converting a datetime/timestamp into a date can become non-obvious. As this helpful documentation points out:
A datetime represents a point in time. It’s absolute: it doesn’t depend on anything. On the contrary, a date is a calendaring concept. It’s a period of time whose bounds depend on the time zone in which the date is considered. As you can see, these two concepts are fundamentally different.
Understanding this difference is a key step towards avoiding time-based bugs. Good luck.
How do you convert datetime/timestamp from one timezone to another timezone?
There are two steps:
-
Create an aware datetime objects from the system time and timezone e.g., to get the current system time in the given timezone:
#!/usr/bin/env python
from datetime import datetime
import pytz
server_timezone = pytz.timezone("US/Eastern")
server_time = datetime.now(server_timezone) # you could pass *tz* directly
Note: datetime.now(server_timezone) works even during ambiguous times e.g., during DST transitions while server_timezone.localize(datetime.now()) may fail (50% chance).
If you are sure that your input time exists in the server’s timezone and it is unique then you could pass is_dst=None to assert that:
server_time = server_timezone.localize(naive_time, is_dst=None)
It raises an exception for invalid times.
If it is acceptable to ignore upto a day error (though typically an error due to DST is around an hour) then you could drop is_dst parameter:
server_time = server_timezone.normalize(server_timezone.localize(naive_time))
.normalize() is called to adjust non-existing times (local time in the gap, during “spring forward” transitions). If the time zone rules haven’t changed; your server shouldn’t generate non-existing times. See “Can I just always set is_dst=True?”
-
Convert an aware datetime object to the target timezone tz:
tz = pytz.timezone("US/Pacific")
server_time_in_new_timezone = server_time.astimezone(tz)
With Python 3.9, the standard lib has all you need: zoneinfo. pytz is not needed anymore (deprecated; -> pytz deprecation shim).
Ex:
from datetime import datetime
from zoneinfo import ZoneInfo
server_timezone = "US/Eastern"
new_timezone = "US/Pacific"
current_time = datetime.now(ZoneInfo(server_timezone))
# current_time_in_new_timezone = ???
current_time_in_new_timezone = current_time.astimezone(ZoneInfo(new_timezone))
That gives you for example
print(current_time.isoformat(timespec='seconds'))
# 2021-10-04T02:42:54-04:00
print(repr(current_time))
# datetime.datetime(2021, 10, 4, 2, 42, 54, 40600, tzinfo=zoneinfo.ZoneInfo(key='US/Eastern'))
print(current_time_in_new_timezone.isoformat(timespec='seconds'))
# 2021-10-03T23:42:54-07:00
print(repr(current_time_in_new_timezone))
# datetime.datetime(2021, 10, 3, 23, 42, 54, 40600, tzinfo=zoneinfo.ZoneInfo(key='US/Pacific'))
In case you want to convert a timestamp from one timezone to another, you can use this code:
from datetime import datetime
from zoneinfo import ZoneInfo
from_timezone = ZoneInfo('Europe/Moscow') # UTC-3
to_timezone = ZoneInfo('Asia/Tbilisi') # UTC-4
dt = datetime.fromtimestamp(timestamp, to_timezone)
result_timestamp = int(dt.replace(tzinfo=from_timezone).timestamp())
For example, if you take timestamp = 529635600 (1986-14-10 04:00:00 in Moscow) and run this code, you will get result_timestamp = 529639200 (1986-14-10 05:00:00 in Tbilisi).
Specifically, given the timezone of my server (system time perspective) and a timezone input, how do I calculate the system time as if it were in that new timezone (regardless of daylight savings, etc)?
import datetime
current_time = datetime.datetime.now() #system time
server_timezone = "US/Eastern"
new_timezone = "US/Pacific"
current_time_in_new_timezone = ???
If you know your origin timezone and the new timezone that you want to convert it to, it turns out to be very straightforward:
-
Make two
pytz.timezoneobjects, one for the current timezone and one for the new timezone e.g.pytz.timezone("US/Pacific"). You can find a list of all official timezones inpytzlibrary:import pytz; pytz.all_timezones -
Localize the datetime/timestamp of interest to the current timezone e.g.
current_timezone = pytz.timezone("US/Eastern")
localized_timestamp = current_timezone.localize(timestamp)
- Convert to new timezone using
.astimezone()on the newly localized datetime/timestamp from step 2 with the desired timezone’s pytz object as input e.g.localized_timestamp.astimezone(new_timezone).
Done!
As a full example:
import datetime
import pytz
# a timestamp I'd like to convert
my_timestamp = datetime.datetime.now()
# create both timezone objects
old_timezone = pytz.timezone("US/Eastern")
new_timezone = pytz.timezone("US/Pacific")
# two-step process
localized_timestamp = old_timezone.localize(my_timestamp)
new_timezone_timestamp = localized_timestamp.astimezone(new_timezone)
# or alternatively, as an one-liner
new_timezone_timestamp = old_timezone.localize(my_timestamp).astimezone(new_timezone)
Bonus: but if all you need is the current time in a specific timezone, you can conveniently pass that timezone directly into datetime.now() to get the current times directly:
datetime.datetime.now(new_timezone)
When it comes to needing timezones conversions generally, I would strongly advise that one should store all timestamps in your database in UTC, which has no daylight savings time (DST) transition. And as a good practice, one should always choose to enable time zone support (even if your users are all in a single time zone!). This will help you avoid the DST transition problem that plagues so much software today.
Beyond DST, time in software can be generally quite tricky. To get a sense of just how difficult it is to deal with time in software in general, here is a potentially enlightening resource: http://yourcalendricalfallacyis.com
Even a seemingly simple operation as converting a datetime/timestamp into a date can become non-obvious. As this helpful documentation points out:
A datetime represents a point in time. It’s absolute: it doesn’t depend on anything. On the contrary, a date is a calendaring concept. It’s a period of time whose bounds depend on the time zone in which the date is considered. As you can see, these two concepts are fundamentally different.
Understanding this difference is a key step towards avoiding time-based bugs. Good luck.
How do you convert datetime/timestamp from one timezone to another timezone?
There are two steps:
-
Create an aware datetime objects from the system time and timezone e.g., to get the current system time in the given timezone:
#!/usr/bin/env python from datetime import datetime import pytz server_timezone = pytz.timezone("US/Eastern") server_time = datetime.now(server_timezone) # you could pass *tz* directlyNote:
datetime.now(server_timezone)works even during ambiguous times e.g., during DST transitions whileserver_timezone.localize(datetime.now())may fail (50% chance).If you are sure that your input time exists in the server’s timezone and it is unique then you could pass
is_dst=Noneto assert that:server_time = server_timezone.localize(naive_time, is_dst=None)It raises an exception for invalid times.
If it is acceptable to ignore upto a day error (though typically an error due to DST is around an hour) then you could dropis_dstparameter:server_time = server_timezone.normalize(server_timezone.localize(naive_time)).normalize()is called to adjust non-existing times (local time in the gap, during “spring forward” transitions). If the time zone rules haven’t changed; your server shouldn’t generate non-existing times. See “Can I just always set is_dst=True?” -
Convert an aware datetime object to the target timezone
tz:tz = pytz.timezone("US/Pacific") server_time_in_new_timezone = server_time.astimezone(tz)
With Python 3.9, the standard lib has all you need: zoneinfo. pytz is not needed anymore (deprecated; -> pytz deprecation shim).
Ex:
from datetime import datetime
from zoneinfo import ZoneInfo
server_timezone = "US/Eastern"
new_timezone = "US/Pacific"
current_time = datetime.now(ZoneInfo(server_timezone))
# current_time_in_new_timezone = ???
current_time_in_new_timezone = current_time.astimezone(ZoneInfo(new_timezone))
That gives you for example
print(current_time.isoformat(timespec='seconds'))
# 2021-10-04T02:42:54-04:00
print(repr(current_time))
# datetime.datetime(2021, 10, 4, 2, 42, 54, 40600, tzinfo=zoneinfo.ZoneInfo(key='US/Eastern'))
print(current_time_in_new_timezone.isoformat(timespec='seconds'))
# 2021-10-03T23:42:54-07:00
print(repr(current_time_in_new_timezone))
# datetime.datetime(2021, 10, 3, 23, 42, 54, 40600, tzinfo=zoneinfo.ZoneInfo(key='US/Pacific'))
In case you want to convert a timestamp from one timezone to another, you can use this code:
from datetime import datetime
from zoneinfo import ZoneInfo
from_timezone = ZoneInfo('Europe/Moscow') # UTC-3
to_timezone = ZoneInfo('Asia/Tbilisi') # UTC-4
dt = datetime.fromtimestamp(timestamp, to_timezone)
result_timestamp = int(dt.replace(tzinfo=from_timezone).timestamp())
For example, if you take timestamp = 529635600 (1986-14-10 04:00:00 in Moscow) and run this code, you will get result_timestamp = 529639200 (1986-14-10 05:00:00 in Tbilisi).