I converted a UNIX timestamp to a human format (sorry I do not know the exact name of it) in a specific timezone (Africa/Algeria) and it evaluated to this: 2020-06-05 19:45:21+01:00. I looked into the datetime module documentation and from what I understood the +01:00, it is the +/-HH:MM offset from the UTC.
What I do not understand is why it is returned with the datetime object given it is already converted to the indicated timezone?
Could someone explain it to me?
Thanks.
POSIX timestamps (Unix time) represent time in seconds since the epoch, 1970-01-01 UTC. No time zone issues involved here. datetime objects on the other hand can be naive (not contain any time zone information) or time zone aware. What you have is a time zone aware datetime object - its string representation prints out as "2020-06-05 19:45:21+01:00". If it had been naive, it would only print "2020-06-05 19:45:21". The repr should also show you a specific time zone, e.g.
print(repr(dt_obj))
>>> datetime.datetime(2020, 6, 5, 19, 45, 21, tzinfo=tzfile('Africa/Algiers'))
The important point is that 2020-06-05 19:45:21+01:00 can be converted back to POSIX timestamp without ambiguity:
from datetime import datetime
datetime.fromisoformat("2020-06-05 19:45:21+01:00").timestamp()
# 1591382721.0
If it wasn't for the +01:00 (no tzinfo), Python would assume that the datetime object belongs in local time, i.e. OS setting; meaning that machines in different time zones would get a different timestamp. I'm on UTC+2, so I would get:
datetime.fromisoformat("2020-06-05 19:45:21").timestamp()
# 1591379121.0
which gives the same timestamp as
datetime.fromisoformat("2020-06-05 19:45:21+02:00").timestamp()
# 1591379121.0
The difference is that with the "+02:00" (tzinfo defined), it is obvious what is happening.