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Re: the Gravity of Python 2

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Date Wed, 08 Jan 2014 21:31:02 -0800
From Ethan Furman <ethan@stoneleaf.us>
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Subject Re: the Gravity of Python 2
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On 01/08/2014 08:34 PM, Chris Angelico wrote:
> On Thu, Jan 9, 2014 at 3:29 PM, Roy Smith <roy@panix.com> wrote:
>> So, I'd like to see your code which generates an aware UTC datetime
>> object in Python.  And then we can argue about whether it's simple or
>> not :-)
>
> Like I said, I don't use the datetime module. But fundamentally, an
> aware datetime represents an instant in time - which is exactly what a
> POSIX timestamp ("time_t") represents. So I can't offer exact code for
> working with them, other than to say that time.time() is precisely
> accomplishing the same job. Maybe there needs to be a recipe posted
> somewhere saying "To create a datetime from a POSIX time, do this".
>
> This is simple:
>
>>>> time.time()
> 1389242048.669482

I agree, and I'm sure Roy also agrees, that that is simple.  However, that is *not* a timezone-aware datetime.  The 
point of having the datetime module is so we all don't have to reroll our own from scratch, and yet this particular (and 
increasingly important) operation wasn't intuitive nor easy.


http://docs.python.org/dev/library/datetime.html?highlight=datetime#datetime.tzinfo
===================================================================================

class datetime.tzinfo

     An abstract base class for time zone information objects. These are used by the datetime and time classes to 
provide a customizable notion of time adjustment (for example, to account for time zone and/or daylight saving time).

class datetime.timezone

     A class that implements the tzinfo abstract base class as a fixed offset from the UTC.

     New in version 3.2.

Objects of these types are immutable.

Objects of the date type are always naive.

An object of type time or datetime may be naive or aware. A datetime object d is aware if d.tzinfo is not None and 
d.tzinfo.utcoffset(d) does not return None. If d.tzinfo is None, or if d.tzinfo is not None but d.tzinfo.utcoffset(d) 
returns None, d is naive. A time object t is aware if t.tzinfo is not None and t.tzinfo.utcoffset(None) does not return 
None. Otherwise, t is naive.
===================================================================================

That is not simple.

This however, may qualify (emphasis added):
===================================================================================
classmethod datetime.utcnow()

     Return the current UTC date and time, with tzinfo None. This is like now(), but returns the current UTC date and 
time, as a naive datetime object. An aware current UTC datetime can be obtained by calling *datetime.now(timezone.utc)*. 
See also now().
===================================================================================

It looks like the .fromtimestamp also accepts tz=timezone.utc, so perhaps that is the simple way to get the timezone 
aware datetime.  I haven't tested, I'm going to bed.  :/

--
~Ethan~

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Thread

Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-07 11:19 +1100
  Re: the Gravity of Python 2 Martijn Faassen <faassen@startifact.com> - 2014-01-07 13:54 +0100
    Re: the Gravity of Python 2 Martijn Faassen <faassen@startifact.com> - 2014-01-07 17:07 +0100
      Re: the Gravity of Python 2 Martijn Faassen <faassen@startifact.com> - 2014-01-07 17:42 +0100
        Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-08 04:00 +1100
          Re: the Gravity of Python 2 Martijn Faassen <faassen@startifact.com> - 2014-01-08 13:36 +0100
            Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-08 23:46 +1100
              Re: the Gravity of Python 2 Martijn Faassen <faassen@startifact.com> - 2014-01-08 16:08 +0100
            Re: the Gravity of Python 2 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-01-09 00:01 +1100
              Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-08 14:08 +0000
              Re: the Gravity of Python 2 Martijn Faassen <faassen@startifact.com> - 2014-01-08 16:22 +0100
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 02:39 +1100
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-08 15:50 +0000
                Re: the Gravity of Python 2 Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-01-09 08:55 +1100
            Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-08 09:15 -0500
              Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-08 14:30 +0000
                Re: the Gravity of Python 2 Martijn Faassen <faassen@startifact.com> - 2014-01-08 16:26 +0100
                Re: the Gravity of Python 2 Kevin Walzer <kw@codebykevin.com> - 2014-01-08 18:42 -0500
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-08 20:27 -0500
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 12:47 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-08 21:25 -0500
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 14:17 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-08 22:35 -0500
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 15:03 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-08 23:29 -0500
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 15:34 +1100
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 15:38 +1100
                Re: the Gravity of Python 2 Ethan Furman <ethan@stoneleaf.us> - 2014-01-08 21:31 -0800
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 17:34 +1100
                Re: the Gravity of Python 2 Ben Finney <ben+python@benfinney.id.au> - 2014-01-09 17:57 +1100
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 18:56 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-09 09:14 -0500
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-10 01:57 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-09 08:21 -0800
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 16:30 +0000
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-09 09:07 -0800
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 18:20 +0000
                Re: the Gravity of Python 2 Ethan Furman <ethan@stoneleaf.us> - 2014-01-09 10:29 -0800
                Re: the Gravity of Python 2 Tim Golden <mail@timgolden.me.uk> - 2014-01-09 16:41 +0000
                RE: the Gravity of Python 2 Nick Cash <nick.cash@npcinternational.com> - 2014-01-09 16:42 +0000
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 16:50 +0000
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-10 07:35 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-09 12:54 -0800
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-10 08:12 +1100
                Re: the Gravity of Python 2 Dan Sommers <dan@tombstonezero.net> - 2014-01-09 15:01 +0000
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-10 02:17 +1100
                Re: the Gravity of Python 2 Ethan Furman <ethan@stoneleaf.us> - 2014-01-09 07:56 -0800
                Re: the Gravity of Python 2 Kushal Kumaran <kushal.kumaran@gmail.com> - 2014-01-09 11:36 +0530
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 08:53 +0000
                Re: the Gravity of Python 2 Ben Finney <ben+python@benfinney.id.au> - 2014-01-09 20:03 +1100
                Re: the Gravity of Python 2 Kushal Kumaran <kushal.kumaran@gmail.com> - 2014-01-09 14:51 +0530
                Re: the Gravity of Python 2 Piet van Oostrum <piet@vanoostrum.org> - 2014-01-09 12:26 +0100
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 09:51 +0000
                Re: the Gravity of Python 2 Ben Finney <ben+python@benfinney.id.au> - 2014-01-10 00:35 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-09 09:32 -0500
                Re: the Gravity of Python 2 Ben Finney <ben+python@benfinney.id.au> - 2014-01-09 14:34 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-08 22:44 -0500
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 14:42 +1100
                Re: the Gravity of Python 2 Piet van Oostrum <piet@vanoostrum.org> - 2014-01-09 15:06 +0100
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-10 01:34 +1100
                Re: the Gravity of Python 2 Roy Smith <roy@panix.com> - 2014-01-09 09:44 -0500
                Re: the Gravity of Python 2 Piet van Oostrum <piet@vanoostrum.org> - 2014-01-09 17:51 +0100
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-10 07:43 +1100
                Time zones and why they change so damned often (was: the Gravity of Python 2) Ben Finney <ben+python@benfinney.id.au> - 2014-01-09 14:54 +1100
                Re: Time zones and why they change so damned often (was: the Gravity of Python 2) Chris Angelico <rosuav@gmail.com> - 2014-01-09 15:14 +1100
                Re: Time zones and why they change so damned often (was: the Gravity of Python 2) Peter Pearson <ppearson@nowhere.invalid> - 2014-01-10 18:22 +0000
                Re: Time zones and why they change so damned often MRAB <python@mrabarnett.plus.com> - 2014-01-10 18:48 +0000
                Re: Time zones and why they change so damned often Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-10 18:53 +0000
                Re: Time zones and why they change so damned often Grant Edwards <invalid@invalid.invalid> - 2014-01-10 19:55 +0000
                Re: Time zones and why they change so damned often Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-01-10 19:45 -0500
                Re: Time zones and why they change so damned often Gene Heskett <gheskett@wdtv.com> - 2014-01-10 21:53 -0500
                Re: Time zones and why they change so damned often (was: the Gravity of Python 2) Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-01-10 19:43 -0500
                Re: Time zones and why they change so damned often (was: the Gravity of Python 2) Roy Smith <roy@panix.com> - 2014-01-10 19:49 -0500
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 07:10 +0000
                Re: Time zones and why they change so damned often Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 07:17 +0000
                Re: Time zones and why they change so damned often Alister <alister.ware@ntlworld.com> - 2014-01-09 12:07 +0000
                Re: Time zones and why they change so damned often Bob Martin <bob.martin@excite.com> - 2014-01-10 07:31 +0000
                Re: Time zones and why they change so damned often Alister <alister.ware@ntlworld.com> - 2014-01-10 09:04 +0000
                Re: Time zones and why they change so damned often Bob Martin <bob.martin@excite.com> - 2014-01-11 07:52 +0000
                Re: Time zones and why they change so damned often Alister <alister.ware@ntlworld.com> - 2014-01-11 11:10 +0000
                Re: Time zones and why they change so damned often Alister <alister.ware@ntlworld.com> - 2014-01-11 11:14 +0000
                Re: Time zones and why they change so damned often Alister <alister.ware@ntlworld.com> - 2014-01-11 11:14 +0000
                Re: Time zones and why they change so damned often (was: the Gravity
 of Python 2) Dave Angel <davea@davea.name> - 2014-01-09 10:34 -0500
                Re: the Gravity of Python 2 Ethan Furman <ethan@stoneleaf.us> - 2014-01-08 17:52 -0800
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 13:09 +1100
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 08:42 +0000
                Re: the Gravity of Python 2 Ethan Furman <ethan@stoneleaf.us> - 2014-01-09 08:01 -0800
                Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-09 18:18 +0000
                Re: the Gravity of Python 2 Ethan Furman <ethan@stoneleaf.us> - 2014-01-09 10:33 -0800
              Re: the Gravity of Python 2 Pedro Larroy <pedro.larroy.lists@gmail.com> - 2014-01-08 15:45 +0100
              Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 01:50 +1100
                Re: the Gravity of Python 2 Grant Edwards <invalid@invalid.invalid> - 2014-01-08 15:06 +0000
                Re: the Gravity of Python 2 Chris Angelico <rosuav@gmail.com> - 2014-01-09 02:31 +1100
              Re: the Gravity of Python 2 Terry Reedy <tjreedy@udel.edu> - 2014-01-08 15:45 -0500
            Re: the Gravity of Python 2 Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-01-08 14:15 +0000

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