CODEWITHSUNDEEP
pythondatetimeepoch
msunbot
msunbot

Reputation: 2001

Convert epoch timestamp to datetime.datetime object

I'd like to convert an epoch time stamp (eg, et =1351036517.179364) to a datetime.datetime object. So far, I've used time.ctime(et) which gives me a string of something like "Fri Oct 5 22:20:33 2012 ".

Eventually, I need the datetime object to compute time difference between two datapoints, the other datapoint is a datetime object as well.

Thanks!

Upvotes: 1

Views: 11618

Answers (3)

Marc
Marc

Reputation: 5518

TLDR

use fromtimestamp as referenced in the documentation

Return the local date corresponding to the POSIX timestamp [...and if tz is supplied...] the timestamp is converted to [supplied] tz’s time zone.

Given a UNIX / EPOCH Timestamp

Here is an example of such a timestamp as generated by python(updated thanks to @jfs and Paul Ganssle)

from datetime import datetime, timezone
epoch = datetime.now(tz=timezone.utc).timestamp()  # example: 1520020585.536527

NOTE: not all epoch's are alike and using time.time() will give seconds elapsed since a platform dependent epoch, where as date.timestamp() gives you what its claims is a POSIX timestamp see caveats below

NOTE: I'm specifically refraining from calling .timestamp()'s output a "POSIX compliant" timestamp. If your application depends on that level of accuracy then you may want to use something other than .timestamp()

NOTE: using datetime.now as it may give a higher precision

NOTE: we could have omitted the tz argument above, but it's good habit to use timezone aware dates, as python 3 may make incorrect assumptions when working with naive dates(or not throw errors where we think it would)

Convert Timestamp to datetime object

Given the timestamp (e.g. 1520020585.536527), we may convert it to a datetime tz aware object using fromtimestamp like so:

from datetime import datetime, timezone
ts = 1520020585.536527  # remember me? I'm the epoch example output from above
utc_date = datetime.fromtimestamp(ts, tz=timezone.utc) # outputs: datetime date object

NOTE: fromtimestamp expects a "POSIX" timestamp, the tz we supply here is only to avoid naive datetime objects. fromtimestamp will perform any needed conversion for the timezone we provide, but what timezone is better than UTC, right?

NOTE: also although the python literature explicitly references the input to fromtimestamp() as a "POSIX" timestamp it is not explicitly referring to the input as "POSIX compliant" and therefore we can only infer what a "POSIX" timestamp is from other parts of its literature, like when it refers to POSIX output as "returned by time.time()"

Upvotes: 1

jfs
jfs

Reputation: 414585

To convert POSIX timestamp to datetime.datetime object that represents time in UTC:

from datetime import datetime, timedelta, timezone

timestamp = 1351036517.179364
utc_time = datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=timestamp)
# -> 2012-10-23 23:55:17.179363+00:00

If your Python version does not support datetime.timezone; you could omit it, to get a naive datetime object in UTC.

I need the datetime object to compute time difference between two datapoints, the other datapoint is a datetime object as well.

If naive datetime objects represent local times that have different UTC offsets than you can't compare them directly otherwise you may get a wrong result. You either need timezone-aware datetime objects or you should convert the datetime objects to UTC first. See

Upvotes: 1

loopbackbee
loopbackbee

Reputation: 23322

It's worthwhile to remember that a timestamp has no associated timezone information. Unix time is unambiguously UTC, but it's not unusual to store local time in Unix-style timestamps. You must check against a known reference to be sure.

If your timestamps are already in UTC (Unix time), you can use Marc B's suggestion of subtract two unix timestamps directly to give you the number of seconds of difference between them. You may then want to create a timedelta, which will allow you to easily manipulate datetimes with it (you can sum or subtract a timedelta to/from a datetime, for example).

datetime.timedelta( seconds= n_seconds )

If your timestamps are in local time, don't subtract them directly, as you'll get potentially incorrect results.

Instead, you should use datetime.fromtimestamp first, attach a timezone to each datetime, and only then subtract them to get the timedelta.

To convert back from a timedelta to the number of seconds, there's timedelta.total_seconds, assuming you're using python 2.7 . If you have an earlier version, you'll have to do the calculation by hand, or pip install datetime

Upvotes: 3

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