问题
I'm working with datetime and find it difficult to understand how timestamp() works, I (in east coast) want to transform the datetime into timestamp, but I found following difference. Can anyone shed somelight how each of the two code works, are they suppose to act differently (roughly a difference of four hours)?
import datetime
datetime.datetime.utcnow().timestamp()
#1590436949.187297
datetime.datetime.now(tz=datetime.timezone.utc).timestamp()
#1590422553.042119
回答1:
The timestamp() method returns a POSIX timestamp / seconds since the epoch which always refers to UTC.
Important: if you pass a naive datetime object to timestamp(), Python will assume that the datetime object holds local time.
That is the issue with datetime.datetime.utcnow(). Although the name utcnow() might suggest otherwise, it gives you a naive datetime object, i.e. it does not "know" it's in UTC. Therefore, if you call the timestamp() method, Python assumes that the datetime object passed to the function is in local time and it is not what you would get from time.time().
On the other hand, in datetime.datetime.now(tz=datetime.timezone.utc).timestamp(), you pass a timezone-aware datetime object to timestamp(). That is correct in the sense that it gives you time.time().
Illustration:
import datetime
import time
import dateutil
localtzname = time.tzname[time.daylight]
# naive:
dt_now = datetime.datetime.now()
# timezone-aware:
dt_now_loc = datetime.datetime.now(dateutil.tz.gettz(localtzname))
dt_now_utc = datetime.datetime.now(tz=datetime.timezone.utc)
# reference:
ts = time.time()
print(dt_now.timestamp())
# 1590424623.226529
print(dt_now_loc.timestamp())
# 1590424623.226529
print(dt_now_utc.timestamp())
# 1590424623.226529
print(ts)
# 1590424623.2265291
As you can see, even though dt_now is naive, Python returns the same timestamp as you get from the localized dt_now_loc or from time.time().
In summary, datetime.datetime.utcnow().timestamp() can be pretty misleading and I would recommend avoiding it.
来源：https://stackoverflow.com/questions/62006348/why-datetime-now-and-datetime-utcnow-return-different-timestamp