python2和python3的datetime时区问题:timezone时间转换

1.python2.7

python2.7的datetime包没有timezone类，用第三方包解决

pip install pytz

import pytz  
from datetime import datetime

u = datetime.utcnow()
u = u.replace(tzinfo=pytz.utc) #NOTE: it works only with a fixed utc offset

print(u)   # prints UTC time
>>> '2020-10-23 06:33:19+00:00'
print(u.astimezone(pytz.timezone("America/New_York")))     # prints another timezone
>>> '2020-10-23 02:33:19-04:00'

t = datetime.now(tz=pytz.timezone('Asia/Shanghai')
print(t)
>>> '2020-10-23 14:33:19+08:00'
print(t.astimezone(pytz.timezone("America/New_York")))
>>> '2020-10-23 02:33:19-04:00'

t = datetime.now()
print(t)
>>> '2020-10-23 14:33:19'
print(t.astimezone(pytz.timezone("America/New_York")))
>>> ValueError: astimezone() cannot be applied to a naive datetime

datetime.replace(tzinfo=tz) 将timezone信息赋给datetime，而不改变日期的值,datetime从一个无时区的状态变成有时区的状态

datetime.astimezone(tzinfo=tz) 时区转换，datetine转换成新时区的值，执行此方法的datetime必须声明过timezone，否则会报cannot apply to a naive datetime

2. python3

python3.2之后的datetime包引入了timezone的类

from datetime import datetime, timedelta, timezone

u = datetime.utcnow()
u = u.replace(tzinfo=timezone.utc) #NOTE: it works only with a fixed utc offset

print(u)   # prints UTC time
>>> '2020-10-23 06:33:19+00:00'
print(u.astimezone(timezone(timedelta(hours=-4), "America/New_York")))    # prints another timezone
>>> '2020-10-23 02:33:19-04:00'

datetime.timezone(offset, name=None)¶ 

offset是timedelta对象，取值限制在 -timedelta(hours=24) and timedelta(hours=24)之间