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Printing datetime as pytz.timezone("Etc/GMT-5") yields incorrect result

Consider the following example, where I take a naive datetime, make it timezone aware in UTC, and then convert to UTC-5:
d1 = datetime.datetime(2019,3,7, 7,45)
d2 = pytz.utc.localize(d1)
print(f'UTC : {d2}')
d3 = d2.astimezone(pytz.timezone('Etc/GMT-5'))
print(f'UTC-5: {d3}')
The output of this is:
UTC : 2019-03-07 07:45:00+00:00
UTC-5: 2019-03-07 12:45:00+05:00
I would have expected the UTC-5 time to be 02:45, but the 5 hour offset is being added to UTC, rather than subtracted.
Questions:
Why is the 'Etc/GMT-5' offset applied to UTC +5 hours instead of -5 hours?
How can I convert from UTC to UTC-5?

You are using pytz, not just Python's datetime.
Like dateutil, pytz uses the Olson tz database.
The Olson tz database defines Etc/GMT+N timezones which conform with the POSIX style:
those zone names beginning with
"Etc/GMT" have their sign reversed from the standard ISO 8601 convention. In
the "Etc" area, zones west of GMT have a positive sign and those east have a
negative sign in their name (e.g "Etc/GMT-14" is 14 hours ahead of GMT.)
So, to convert UTC to a timezone with offset -5 you could use Etc/GMT+5:
import datetime as DT
import pytz
naive = DT.datetime(2019, 3, 7, 7, 45)
utc = pytz.utc
gmt5 = pytz.timezone('Etc/GMT+5')
print(utc.localize(naive).astimezone(gmt5))
# 2019-03-07 02:45:00-05:00

Apparently, in posix style systems, you have to use the inverse of the timezone offset. That means if you want to get -5, you have to use GMT+5.
d3 = d2.astimezone(pytz.timezone('Etc/GMT+5'))
prints
UTC-5: 2019-03-07 02:45:00-05:00
Otherwise, you have to pass the posix_offset as true. This is in dateutil documentation;
There is one notable exception, which is that POSIX-style time zones
use an inverted offset format, so normally GMT+3 would be parsed as an
offset 3 hours behind GMT. The tzstr time zone object will parse this
as an offset 3 hours ahead of GMT. If you would like to maintain the
POSIX behavior, pass a True value to posix_offset.
https://dateutil.readthedocs.io/en/stable/tz.html#dateutil.tz.tzstr

How to compute the time difference between two time zones in python?

How can I compute the time differential between two time zones in Python? That is, I don't want to compare TZ-aware datetime objects and get a timedelta; I want to compare two TimeZone objects and get an offset_hours. Nothing in the datetime library handles this, and neither does pytz.

Here is a solution using the Python library Pytz which solves the issue of ambiguous times at the end of daylight saving time.
from pytz import timezone
import pandas as pd
def tz_diff(date, tz1, tz2):
'''
Returns the difference in hours between timezone1 and timezone2
for a given date.
'''
date = pd.to_datetime(date)
return (tz1.localize(date) -
tz2.localize(date).astimezone(tz1))\
.seconds/3600
The examples below calculate the difference in hours between UTC and Australia time for the first of January and first of June respectively. Notice how daylight savings are taken into consideration.
utc = timezone('UTC')
aus = timezone('Australia/Sydney')
tz_diff('2017-01-01', utc, aus)
# 11.0
tz_diff('2017-06-01', utc, aus)
# 10.0
Thanks

The first thing you have to know is that the offset between two time zones depends not only on the time zones in question, but on the date you're asking about. For example, the dates on which Daylight Savings Time began and ended changed in the US in 2007. While fundamental time zone logistics change only infrequently in any single location, the rate of change globally is impossible to ignore. Therefore, you have to incorporate the date in question into your function.
Having completed the necessary preface, the actual function isn't too hard to write if you take advantage of the pendulum library. It should look something like this:
import pendulum
def tz_diff(home, away, on=None):
"""
Return the difference in hours between the away time zone and home.
`home` and `away` may be any values which pendulum parses as timezones.
However, recommended use is to specify the full formal name.
See https://gist.github.com/pamelafox/986163
As not all time zones are separated by an integer number of hours, this
function returns a float.
As time zones are political entities, their definitions can change over time.
This is complicated by the fact that daylight savings time does not start
and end on the same days uniformly across the globe. This means that there are
certain days of the year when the returned value between `Europe/Berlin` and
`America/New_York` is _not_ `6.0`.
By default, this function always assumes that you want the current
definition. If you prefer to specify, set `on` to the date of your choice.
It should be a `Pendulum` object.
This function returns the number of hours which must be added to the home time
in order to get the away time. For example,
```python
>>> tz_diff('Europe/Berlin', 'America/New_York')
-6.0
>>> tz_diff('Europe/Berlin', 'Asia/Kabul')
2.5
```
"""
if on is None:
on = pendulum.today()
diff = (on.set(tz=home) - on.set(tz=away)).total_hours()
# what about the diff from Tokyo to Honolulu? Right now the result is -19.0
# it should be 5.0; Honolulu is naturally east of Tokyo, just not so around
# the date line
if abs(diff) > 12.0:
if diff < 0.0:
diff += 24.0
else:
diff -= 24.0
return diff
As stated in the documentation, you may not get a stable result for this between any two given locations as you sweep across the days of the year. However, implementing a variant which chooses the median result over the days of the current year is an exercise left for the reader.

Here's another solution:
from datetime import datetime
from pytz import timezone
from dateutil.relativedelta import relativedelta
utcnow = timezone('utc').localize(datetime.utcnow()) # generic time
here = utcnow.astimezone(timezone('US/Eastern')).replace(tzinfo=None)
there = utcnow.astimezone(timezone('Asia/Ho_Chi_Minh')).replace(tzinfo=None)
offset = relativedelta(here, there)
offset.hours
Here what we're doing is converting a time to two different time zones. Then, we remove the time zone information so that when you calculate the difference between the two using relativedelta, we trick it into thinking that these are two different moments in time instead of the same moment in different time zones.
The above result will return -11, however this amount can change throughout the year since US/Eastern observes DST and Asia/Ho_Chi_Minh does not.

I created two functions to deal with timezone.
import datetime
import pytz
def diff_hours_tz(from_tz_name, to_tz_name, negative=False):
"""
Returns difference hours between timezones
res = diff_hours_tz("UTC", "Europe/Paris") : 2
"""
from_tz = pytz.timezone(from_tz_name)
to_tz = pytz.timezone(to_tz_name)
utc_dt = datetime.datetime.now(datetime.timezone.utc)
dt_from = dt_to = datetime.datetime.utcnow()
dt_from = from_tz.localize(dt_from)
dt_to = to_tz.localize(dt_to)
from_d = dt_from - utc_dt
if from_d.days < 0:
return diff_hours_tz(to_tz_name, from_tz_name, True)
dt_delta = dt_from - dt_to
negative_int = -1 if negative else 1
return int(dt_delta.seconds/3600)*negative_int
def dt_tz_to_tz(dt, from_tz_name, to_tz_name):
"""
Apply difference hours between timezones to a datetime object
dt_new = dt_tz_to_tz(datetime.datetime.now(), "UTC", "Europe/Paris")
"""
hours = diff_hours_tz(from_tz_name, to_tz_name)
return dt+datetime.timedelta(hours=hours)
# Usage example
res = diff_hours_tz("Europe/Paris", "America/New_York")
# Result : -6
res = diff_hours_tz("UTC", "Europe/Paris")
# Result : 2
now = datetime.datetime.now()
# Result : 2019-06-18 15:10:31.720105
dt_new = dt_tz_to_tz(now, "UTC", "Europe/Paris")
# Result : 2019-06-18 17:10:31.720105
dt_new = dt_tz_to_tz(now, "Europe/Paris", "America/New_York")
# Result : 2019-06-18 09:10:31.720105
dt_new = dt_tz_to_tz(now, "America/New_York", "Europe/Paris")
# Result : 2019-06-18 21:10:31.720105
I hope it will help !

Here is a code snippet to get the difference between UTC and US/Eastern, but it should work for any two timezones.
# The following algorithm will work no matter what is the local timezone of the server,
# but for the purposes of this discussion, let's assume that the local timezone is UTC.
local_timestamp = datetime.now()
# Assume that utc_timestamp == 2019-01-01 12:00.
utc_timestamp = pytz.utc.localize(local_timestamp)
# If it was 12:00 in New York, it would be 20:00 in UTC. So us_eastern_timestamp is a UTC
# timestamp with the value of 2019-01-01 20:00.
us_eastern_timestamp = timezone("US/Eastern").localize(local_timestamp).astimezone(pytz.utc)
# delta is a Python timedelta object representing the interval between the two timestamps,
# which, in our example, is -8 hours.
delta = utc_timestamp - us_eastern_timestamp
# In the last line, we convert the timedelta into an integer representing the number of
# hours.
print round(delta.total_seconds() / 60.0 / 60.0)

(tz_from.localize(date) - tz_to.localize(date)).seconds/3600.0
Where tz_from and tz_to are the starting and ending timezones. You must specify a particular date.

from datetime import datetime
from zoneinfo import ZoneInfo
dt = datetime.now() # 2020-09-13
tz0, tz1 = "Europe/Berlin", "US/Eastern" # +2 vs. -4 hours rel. to UTC
utcoff0, utcoff1 = dt.astimezone(ZoneInfo(tz0)).utcoffset(), dt.astimezone(ZoneInfo(tz1)).utcoffset()
print(f"hours offset between {tz0} -> {tz1} timezones: {(utcoff1-utcoff0).total_seconds()/3600}")
>>> hours offset between Europe/Berlin -> US/Eastern timezones: -6.0
a way to do this with Python 3.9's standard library.

Compute midnight timestamp in UTC +0 using DateTime python 3.5

I need to scrap an online database which contain +/- 24h of data at fixed interval using an API query which contain a timestamp. Because i don't know where the server is choose something simple like midnigth UTC.
I found lot of documentation on SO to compute UTC aware of local zone. I'm actually using this protocole to get actual UTC Date :
import datetime
myDate = datetime.datetime.now(datetime.timezone.utc)
print("TZ INFO = ", myDate.tzinfo) # return UTC+00:00
print("DATE ", myDate) # return 2017-07-08 14:14:24.137003+00:00
print("ISO DATE = ", myDate.timestamp()) # return 1499523264.137003
First question, why the timestamp() returned take in account the local timezone : 1499523264.137003 is equal to ~16h15, so UTC +2 corresponding to France Zone. Why timestamp() doesn't return only the UTC + 0 timestamp ? How can i get an UTC + 0 timestamp ?
Second question, i try to generate a midnight date to query the API, so like i saw on many post on SO, i try to use the replace() function :
myDate = myDate.replace(hour=0, minute=0, second=0,microsecond=0).astimezone(pytz.utc)
print (myDate) # return 2017-07-08 00:00:00+00:00
But when i try to print (myDate.timestamp()) return another time a UTC + 2 timestamp, so 2AM of 2017-07-08. How can i get midnight UTC + 0 timestamp easily ?

I would suggest using the pendulum module since it makes timezone and date calculations easy to perform.
pendulum is aware of daylight savings time schemes, as indicated here for London and Paris. It can also provide the UTC time shorn of an adjustment for daylight savings time. When you need to provide an adjustment to UTC you can simply using the replace method in conjunction with UTC.
>>> import pendulum
>>> pendulum.create(2017,7,9,0,0,0,0,'Europe/London')
<Pendulum [2017-07-09T00:00:00+01:00]>
>>> pendulum.create(2017,7,9,0,0,0,0,'Europe/Paris')
<Pendulum [2017-07-09T00:00:00+02:00]>
>>> pendulum.create(2017,7,9,0,0,0,0,'UTC')
<Pendulum [2017-07-09T00:00:00+00:00]>
>>> t = pendulum.create(2017,7,9,0,0,0,0,'UTC')
>>> t.replace(hour=+2)
<Pendulum [2017-07-09T02:00:00+00:00]>

How to convert tomorrows (at specific time) date to a timestamp

How can i actually create a timestamp for the next 6 o'clock, whether that's today or tomorrow?
I tried something with datetime.datetime.today() and replace the day with +1 and hour = 6 but i couldnt convert it into a timestamp.
Need your help

To generate a timestamp for tomorrow at 6 AM, you can use something like the following. This creates a datetime object representing the current time, checks to see if the current hour is < 6 o'clock or not, creates a datetime object for the next 6 o'clock (including adding incrementing the day if necessary), and finally converts the datetime object into a timestamp
from datetime import datetime, timedelta
import time
# Get today's datetime
dtnow = datetime.now()
# Create datetime variable for 6 AM
dt6 = None
# If today's hour is < 6 AM
if dtnow.hour < 6:
# Create date object for today's year, month, day at 6 AM
dt6 = datetime(dtnow.year, dtnow.month, dtnow.day, 6, 0, 0, 0)
# If today is past 6 AM, increment date by 1 day
else:
# Get 1 day duration to add
day = timedelta(days=1)
# Generate tomorrow's datetime
tomorrow = dtnow + day
# Create new datetime object using tomorrow's year, month, day at 6 AM
dt6 = datetime(tomorrow.year, tomorrow.month, tomorrow.day, 6, 0, 0, 0)
# Create timestamp from datetime object
timestamp = time.mktime(dt6.timetuple())
print(timestamp)

To get the next 6 o'clock while handling timezones that observe Daylight saving time (DST) correctly:
from datetime import datetime, time, timedelta
import pytz # $ pip install pytz
from tzlocal import get_localzone # $ pip install tzlocal
DAY = timedelta(1)
local_timezone = get_localzone()
now = datetime.now(local_timezone)
naive_dt6 = datetime.combine(now, time(6))
while True:
try:
dt6 = local_timezone.localize(naive_dt6, is_dst=None)
except pytz.NonExistentTimeError: # no such time today
pass
except pytz.AmbiguousTimeError: # DST transition (or similar)
dst = local_timezone.localize(naive_dt6, is_dst=True)
std = local_timezone.localize(naive_dt6, is_dst=False)
if now < min(dst, std):
dt6 = min(dst, std)
break
elif now < max(dst, std):
dt6 = max(dst, std)
break
else:
if now < dt6:
break
naive_dt6 += DAY
Once you have an aware datetime object that represents the next 6 o'clock in the local timezone, it is easy to get the timestamp:
timestamp = dt6.timestamp() # in Python 3.3+
Or on older Python versions:
timestamp = (dt6 - datetime(1970, 1, 1, tzinfo=pytz.utc)).total_seconds()
See Converting datetime.date to UTC timestamp in Python.
The solution works even if any of the following happens:
python (e.g., time.mktime() calls) has no access to a historical timezone database on a given system (notably: Windows)—pytz provides a portable access to the tz database
there is a DST transition between now and the next X hour (where X is 6am in your case) or if the UTC offset for the local timezone has changed for any other reason—"naive datetime object + relativedelta" solution would fail silently to find the correct number of seconds but timezone-aware datetime objects could enable to find the right time difference
the nominal next X hour (today or tomorrow) does not exist or ambiguous in the local time zone (most often, it happens during DST transitions—every year in many timezones). Solutions using dateutil tzinfos or pytz-based solutions that use .localize() without is_dst=None would fail silently. The application should handle NonExistentTimeError and AmbiguousTimeError exceptions explicitly in this case
the current time is after the first time an ambiguous X hour happens in the local timezone but before the second time the X hour happens —"rrule + return min(localize(ndt, is_dst=True), localize(ndt, is_dst=False))" solution would fail silently. The min/max code in the AmbiguousTimeError clause above handles it correctly.

In Python, using win32api doesn't set the correct date

I am trying to set system date (not time) using following code. I want to set the current time to the new date. Following is a sample code and I found the time is not correct after change.
day = 20
month = 3
year = 2010
timetuple = time.localtime()
print timetuple
print timetuple[3], timetuple[4], timetuple[5]
win32api.SetSystemTime(year, month, timetuple[6]+1,
day, timetuple[3], timetuple[4], timetuple[5], 1)

You are setting the system time from the localtime timestamp. The latter is adjusted for the local timezone, while SetSystemTime requires you to use the UTC timezone.
Use time.gmtime() instead:
tt = time.gmttime()
win32api.SetSystemTime(year, month, 0, day,
tt.tm_hour, tt.tt_min, tt.tt_sec, 0)
You then also avoid having to deal with whether or not you are in summer time (DST) now, vs. March when you would be in winter time.
Alternatively you can use a datetime.datetime.utcnow() call and get the millisecond parameter as a bonus:
import datetime
tt = datetime.datetime.utcnow().time()
win32api.SetSystemTime(year, month, 0, day,
tt.hour, tt.minute, tt.second, tt.microsecond//1000)
Note that I left the weekday item set to 0 in both examples; it is ignored when calling SetSystemTime. If it was not ignored, then your code example had the value wrong; the Python value ranges from 0 to 6 for Monday through to Sunday, while the Win32 API wants 1 through to 7 for Sunday through to Saturday. You'd have to add 2 and use modulo 7:
win32_systemtime_weekday = (python_weekday + 2) % 7)