I am trying to understand how datetime objects behave in python
>>> import pytz
>>> from datetime import datetime
>>> now = datetime.now()
>>> now
datetime.datetime(2022, 10, 11, 22, 9, 14, 169110)
>>> now.tzinfo
# even though there is no tzinfo, when converted to utc, it shows 20:09
>>> now.astimezone(pytz.utc)
datetime.datetime(2022, 10, 11, 20, 9, 14, 169110, tzinfo=<UTC>)
>>> pytz.utc.localize(now)
datetime.datetime(2022, 10, 11, 22, 9, 14, 169110, tzinfo=<UTC>)
I am trying to understand the reason of the change in the time with line now.astimezone(pytz.utc) since the datetime object was naive in the first place.
Related
Given a datetime.datetime object like that:
datetime.datetime(2022, 2, 22, 9, 24, 20, 386060)
I get client timezone offset in such format: "+0300" and need to represent the datetime.datetime object considering this offset.
For example, the object above should look like this:
datetime.datetime(2022, 2, 22, 12, 24, 20, 386060)
IIUC, you have a datetime object that represents UTC and want to convert to a UTC offset of 3 hours. You can do that like
import datetime
dt = datetime.datetime(2022, 2, 22, 9, 24, 20, 386060)
# assuming this is UTC, we need to set that first
dt = dt.replace(tzinfo=datetime.timezone.utc)
# now given the offset
offset = "+0300"
# we can convert like
converted = dt.astimezone(datetime.datetime.strptime(offset, "%z").tzinfo)
>>> converted
datetime.datetime(2022, 2, 22, 12, 24, 20, 386060, tzinfo=datetime.timezone(datetime.timedelta(seconds=10800)))
Assume this is my date time stamp list:
[datetime.datetime(2017, 11, 17, 9, 33, 11), datetime.datetime(2017, 11, 17, 9, 33, 36), datetime.datetime(2017, 11, 17, 9, 33, 48)]
A lot of examples have been given for converting these values to epoch, but the values are in GMT.
How do we convert it to Epoch Local time?
To put it in simpler words. The general epoch conversion coverts the given date into epoch considering that the datetime given is in GMT. But the given date time is localtime!
>>> x = datetime.datetime(2017, 11, 17, 9, 33, 36)
>>> x.timestamp()
1510882416.0
>>> x.ctime()
'Fri Nov 17 09:33:36 2017'
You can use this:
l = [datetime.datetime(2017, 11, 17, 9, 33, 11), datetime.datetime(2017, 11, 17, 9, 33, 36), datetime.datetime(2017, 11, 17, 9, 33, 48)]
epo = [x.strftime('%s') for x in l]
print(epo)
# ['1510898591', '1510898616', '1510898628']
You can try arrow lib:
import arrow
import datetime
x = datetime.datetime(2017, 11, 17, 9, 33, 36)
time = arrow.get(x, 'local').shift(hours=-6) // here you can change hours to what you want
print time
>>2017-11-17T03:33:36+00:00
time = time.format('YYYY-MM-DD HH:mm:ss')
print time
>>2017-11-17 03:33:36
I'm trying to modify a datetime based on a timezone on save and on load the following way:
An input datetime, along with a input timezone are sent to the server and the server should update the datetime to reflect the timezone. So when it saves in the database (PostregSQL), the UTC time is saved (after the offset caused by the timezone, of course).
To reflect this here's a simpler example that fails in the same way:
Some imports:
>>> import datetime
>>> import pytz
>>> from apps.myapp.models import Project
Creating the two inputs:
>>> input_date = timezone.now()
>>> input_date
datetime.datetime(2017, 2, 7, 16, 7, 14, 377429, tzinfo=<UTC>)
>>> current_tz = pytz.timezone('America/New_York')
>>> current_tz
<DstTzInfo 'America/New_York' LMT-1 day, 19:04:00 STD>
As you can see, the timezone is not 5h (24 - 19 = 5), but 4h56. At this stage I'm thinking that's OK, it may be related to the Daylight Saving Time.
Now I'm replacing the timezone on the input date:
>>> input_date = input_date.replace(tzinfo=current_tz)
>>> input_date
datetime.datetime(2017, 2, 7, 16, 7, 14, 377429, tzinfo=<DstTzInfo 'America/New_York' LMT-1 day, 19:04:00 STD>)
As expected, the time hasn't changed, but the timezone has, which is fine.
I'll assign this value to a project (the launch_date is a DateTimeField without any specific option):
>>> project = Project.objects.get(pk=1)
>>> project.launch_date
datetime.datetime(2017, 1, 14, 8, 53, 57, 241718, tzinfo=<UTC>)
>>> project.launch_date = input_date
>>> project.launch_date
datetime.datetime(2017, 2, 7, 16, 7, 14, 377429, tzinfo=<DstTzInfo 'America/New_York' LMT-1 day, 19:04:00 STD>)
Now I'll save this into (and refresh from) the database, leaving Django/PostgreSQL do the maths:
>>> project.save()
>>> project.refresh_from_db()
>>> project.launch_date
datetime.datetime(2017, 2, 7, 21, 3, 14, 377429, tzinfo=<UTC>)
As expected the date is now 4h56 ahead of the previous date. I'm trying now to get back the local time:
>>> project.launch_date.astimezone(current_tz)
datetime.datetime(2017, 2, 7, 16, 3, 14, 377429, tzinfo=<DstTzInfo 'America/New_York' EST-1 day, 19:00:00 STD>)
>>> input_date
datetime.datetime(2017, 2, 7, 16, 7, 14, 377429, tzinfo=<DstTzInfo 'America/New_York' LMT-1 day, 19:04:00 STD>)
This time, the offset is perfectly 5h. And I'm missing 4 minutes.
3 questions here:
Where is this 4 minutes coming from?
Why is astimezone not using the 4 minutes as well?
How can a datetime be converted to UTC, saved, loaded and converted back to local?
pytz time zones are a little weird, as you can see by multiple questions on StackOverflow. They often won't show the correct offset or timezone name unless they are allowed to adjust themselves to the datetime they are being paired with. Here is what the documentation has to say:
This library only supports two ways of building a localized time. The first is to use the localize() method provided by the pytz library. This is used to localize a naive datetime (datetime with no timezone information):
The second way of building a localized time is by converting an existing localized time using the standard astimezone() method:
Unfortunately using the tzinfo argument of the standard datetime constructors “does not work” with pytz for many timezones.
It does not say so explicitly, but using replace has the same problem as using the datetime constructor.
To accomplish what your code was doing without the 4-minute discrepancy, you can use localize():
>>> input_date
datetime.datetime(2017, 2, 7, 16, 7, 14, 377429, tzinfo=<UTC>)
>>> current_tz.localize(input_date.replace(tzinfo=None))
datetime.datetime(2017, 2, 7, 16, 7, 14, 377429, tzinfo=<DstTzInfo 'America/New_York' EST-1 day, 19:00:00 STD>)
I suspect that's a bug though, and you really want to do a timezone conversion from UTC:
>>> input_date.astimezone(current_tz)
datetime.datetime(2017, 2, 7, 11, 7, 14, 377429, tzinfo=<DstTzInfo 'America/New_York' EST-1 day, 19:00:00 STD>)
I have a date string like - 2015-01-05T10:30:47-0800,
It looks to me that this is some timezone because of the offset. How can I get a date string which is in the UTC timezone from the above date string.
I tried the following -
datestring = '2015-01-05T10:30:47-0800'
from dateutil import parser
d = parser.parse(datestring) # datetime.datetime(2015, 1, 5, 10, 30, 47, tzinfo=tzoffset(None, -28800))
import pytz
d.astimezone(pytz.timezone('UTC')) # datetime.datetime(2015, 1, 5, 18, 30, 47, tzinfo=<UTC>)
EDIT -
The above code returns the correct answer. My bad!
Try this:
>>> import dateutil.parser
>>> d = dateutil.parser.parse('2015-01-05T10:30:47-0800')
>>> d.astimezone(dateutil.tz.tzutc())
datetime.datetime(2015, 1, 5, 18, 30, 47, tzinfo=tzutc())
Consider:
now = datetime.datetime.now()
now
datetime.datetime(2009, 11, 6, 16, 6, 42, 812098)
How would I create a new datetime object (past) and minus n values from the hours?
Use timedelta in the datetime module:
import datetime
now = datetime.datetime.now()
past = now - datetime.timedelta(hours=10)
Use a timedelta object.
>>> now = datetime.datetime.now()
>>> now
datetime.datetime(2009, 11, 6, 16, 35, 50, 593000)
>>> ten_hours = datetime.timedelta(hours=10)
>>> now + ten_hours
datetime.datetime(2009, 11, 7, 2, 35, 50, 593000)
>>> now - ten_hours
datetime.datetime(2009, 11, 6, 6, 35, 50, 593000)
Use a timedelta object.
from datetime import datetime
back = datetime.now() - timedelta(hours=10)