About this article

In this article, I spelled out how to get the current date and time in Python, taking into account the time difference. I've noted how it works in both Python2 and Python3, using only the standard module (datetime).

The detailed description of the various methods and objects of the datetime module is omitted.

Trigger

I implemented a web app in Python and was trying to run it on Heroku. I'm trying to implement a feature and need to get the current date and time.

If you just try to get the current time, you get the system time on the Heroku server. On the Heroku server, the system time is running at +00: 00 (UTC).

So what if you just run the app in Japan and just use Heroku's system time? When the function is operated by the app and the time is acquired, it will be 12:00 Japan time. Then, Heroku's system time is 3:00. Japan time is 12:00, but the app will proceed as 3:00.

Hmmm, this is not good ... (Especially for calendars and reminders.) If you just add 9 hours, it will be solved immediately, but I want to make sure that the exact date and time is returned without depending on the time zone setting of the server.

procedure

First, I'll show you the whole code that works for now.

import datetime

# UTC (Coordinated Universal Time)Get the time of
time_now_utc = datetime.datetime.utcnow()
print(time_now_utc)
# 2020-10-10 14:51:22.910110

#Japan is 9 hours ahead of UTC
time_dt_ja = datetime.timedelta(hours=9)
print(time_dt_ja)
# 9:00:00

#If you add 9 hours to UTC, it will be Japan time.
time_now_ja = time_now_utc + time_dt_ja
print(time_now_ja)
# 2020-10-10 23:51:22.910110

1. First, get UTC (Coordinated Universal Time)

If you get the date and time with datetime.datetime.utcnow (), you will get the same result (UTC) regardless of whether the time zone of the operating machine is Japan, United Kingdom, or the United States. (If it is datetime.datetime.now (), the result will change depending on the time zone setting of the running machine.) First of all, this will make up for the difference in the time zone setting of the operating machine.

time_now_utc = datetime.datetime.utcnow()

print(time_now_utc)
# 2020-10-10 14:51:22.910110

type(time_now_utc)
# <class 'datetime.datetime'>

Here you get the datetime object.

2. Next, prepare for the calculation to apply the time difference

timedelta Prepare the object. The datetime object is the ** time information ** object, and the timedelta is the ** time information ** object.

time_dt_test = datetime.timedelta(days=1, seconds=1, microseconds=1, milliseconds=1, minutes=1, hours=1, weeks=1)

print(time_dt_test)
# 8 days, 1:01:01.001001

type(time_dt_test)
# <class 'datetime.timedelta'>

If you specify the day (week, day) and hour (hour, minute, second) in this way, it will be converted into day and time information.

3. Finally the calculation

The datetime and timedelta objects can be operated on by + -. By adding 9 hours to UTC, it becomes Japan time, so

time_now_ja = time_now_utc + time_dt_ja

print(time_now_ja)
# 2020-10-10 23:51:22.910110

After that, use the datetime method as appropriate.

print(time_now_ja.strftime("%Y year%m month%d day"))
#October 10, 2020

Regarding strftime (), it seems that there are various format codes as well as % Y, % d, % m. See official documentation for details https://docs.python.org/ja/3/library/datetime.html#strftime-strptime-behavior

Digression

According to the official documentation, getting UTC is better than datetime.datetime.utcnow () datetime.datetime.now (datetime.timezone.utc) seems to be recommended.

https://docs.python.org/ja/3/library/datetime.html

However, Python2 doesn't seem to have a timezone object.

(But the timezone relationship is probably much smarter to implement using the timezone object.)

Get the current date and time in Python, considering the time difference