Determine start and end time of current day (UTC -> EST -> UTC) ; Python

The first step of getting current time as UTC and converting it to EST seems a bit pointless. Do you use that time for anything?

Other than that it seems rather straighforward. You want to get the start and end of a day EST in UTC, so you create them and convert them to UTC. That's not so complicated. :-)

You might want to look at your matching routines though, so that you can use the start of today as the lower value, and the start of tomorrow as the higher, so you don't have to deal with that 23:59:59.9999 time.

Update:

From my original understanding of your question, this is what you want to do:

First you want to get the current date as it is in UTC (so at 11pm EST the 12st, you want the 22nd, as it is the 22nd in UTC then.

>>> from datetime import datetime
>>> today = datetime.utcnow().date()
>>> today
datetime.date(2013, 2, 21)

Secondly you want 00:00:00 of that day in UTC, as start for a search.

>>> from dateutil import tz
>>> start = datetime(today.year, today.month, today.day, tzinfo=tz.tzutc())
datetime.datetime(2013, 2, 21, 0, 0, tzinfo=tzutc())

Except that you want to know what that time is in New York:

>>> from dateutil import tz
>>> est = tz.gettz('America/New_York')
>>> start = start.astimezone(est)
>>> start
datetime.datetime(2013, 2, 20, 19, 0, tzinfo=tzfile('/usr/share/zoneinfo/America/New_York'))

And you also want tomorrow as the end:

>>> from datetime import timedelta
>>> end = start + timedelta(1)
>>> end
datetime.datetime(2013, 2, 21, 19, 0, tzinfo=tzfile('/usr/share/zoneinfo/America/New_York'))

Summary:

today = datetime.utcnow().date()
start = datetime(today.year, today.month, today.day, tzinfo=tz.tzutc()).astimezone(est)
end = start + timedelta(1)

I would definitely give Delorean a look, to solve your problem would follow a few steps.

You first need to parse your string. Excellent use the Delorean parse method.

>>> from delorean import parse
>>> d = parse("Wed, 20 Feb 2013 03:51:39 +0000")
>>> d
Delorean(datetime=2013-02-20 03:51:39+00:00, timezone=UTC)

Once you have the datetime that you parsed in a Delorean object you simply convert to EST

>>> d = d.shift('US/Eastern')
>>> d
Delorean(datetime=2013-02-19 22:51:39-05:00, timezone=US/Eastern)

Albeit pointless. You never use it for anything in your question, but super easy with Delorean.

Then you get the time now in EST

from delorean import Delorean

>>> d1 = Delorean(timezone="US/Eastern")
>>> d1
Delorean(datetime=2013-02-21 00:35:56.405256-05:00, timezone=US/Eastern)

Now for the truncation step.

>>> d.truncate('day')
Delorean(datetime=2013-02-21 00:00:00-05:00, timezone=US/Eastern)

do the simple shift as above to UTC.

Now get the end of day.

d = d.next_day(1) # move to the next day

Then to shift back one second. Something that the library needs I will be updating this. Simply get the datetime from the Delorean example by asking for it with datetime attribute.

d.datetime - timedelta(seconds=1)
datetime.datetime(2013, 2, 21, 23, 59, 59, tzinfo=<DstTzInfo 'US/Eastern' EST-1 day, 19:00:00 STD>)

Goodluck, but this library should simply your dealing with datetime operations :)

This is only a partial answer, because the rest has been covered well. I struggled with this for a while, as some technologies have inclusive searches, and I don't want to include any data from the first microsecond of the next day.

My solution for finding the end of day time quickly and correctly is this:

reference_time.replace(hour=0, minute=0, second=0, microsecond=0) + timedelta(days=1,microseconds=-1)

use datetime pytz will solve your problem.

def get_start_and_end():
    tz = pytz.timezone('Asia/Shanghai')
    today = datetime.now(tz=tz)
    start = today.replace(hour=0, minute=0, second=0, microsecond=0)
    end = start + timedelta(1)

    return start, end