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| References | (16 earlier) <52CE3416.9090501@stoneleaf.us> <CAPTjJmp6OfeMAZwbjAhT+N7dm_q3sj01cuCK9Vp7RFSf8bKnWQ@mail.gmail.com> <7wiottej72.fsf@benfinney.id.au> <mailman.5244.1389254198.18130.python-list@python.org> <roy-5C5BD9.09142209012014@news.panix.com> |
|---|---|
| Date | 2014-01-10 01:57 +1100 |
| Subject | Re: the Gravity of Python 2 |
| From | Chris Angelico <rosuav@gmail.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.5260.1389279482.18130.python-list@python.org> (permalink) |
On Fri, Jan 10, 2014 at 1:14 AM, Roy Smith <roy@panix.com> wrote:
> In article <mailman.5244.1389254198.18130.python-list@python.org>,
> Chris Angelico <rosuav@gmail.com> wrote:
>
>> What can you (Roy), with your use-case, achieve with datetime that
>> you can't achieve (at least reasonably easily) with a timestamp?
Thanks for this collection! Now we can discuss.
> As I'm mentioned several times, when you print a datetime, you get
> something that's human friendly. When you print a timestamp (i.e. a
> float), you get a lot of digits. I don't know about you, but I can't
> look at 1389274842 and get any feel for whether that was in the middle
> of the night or at 5 in the afternoon, near our peak traffic time. Nor
> can I tell if it was today, yesterday, last month, or a week from next
> Tuesday.
Sure. There is a lot of value in having a class that knows how it
should be displayed. I'm not sure the current datetime repr is good
for anything more than debugging, but I agree that
"datetime.datetime(2014, 1, 9, 5, 57, 59, 929176)" is more likely to
be useful than a raw number.
> Datetimes make it easy to do things like, "find the time of the
> preceding (or following) midnight". Or, "what month is this timestamp
> part of?" These are operations we need to do a lot, to answer questions
> like, "How many unique users did we have on a given day?", or "Which
> monthly database archive file do I need to grab to get information about
> this historical event?"
That's true; the same operations done with timestamps look like this:
>>> ts = time.time()
>>> ts_at_midnight_utc = ts - ts%86400
>>> ts_at_midnight_utc
1389225600.0
Not nearly as obvious what's happening. And months are more
complicated still, so it's probably easiest to use strftime:
>>> time.strftime("%Y%m",time.gmtime(ts))
'201401'
which could then be used as a lookup key for a counter or whatever.
Yep, that's not as clean as simply calling a method.
> Datetimes are self-documenting. If I'm in the python shell and have
> something called t, I can do help(t) or dir(t) to find out what
> operations it has.
Partly true, but not everything's there. For instance, if you have a
list of strings, you won't find a way to join them together in its
help() or dir(), and yet it's a fundamental and very important
operation.
> Datetimes are self-describing. If I have a datetime or a timedelta, I
> know what I've got. I've written more than one bug where I assumed a
> number somebody handed me was in seconds but it turned out to be in ms.
> That can never happen with a timedelta. We do a lot of stuff in
> javascript, where times are ms, so this is a common problem for us.
Sure. Though that's no different from other cases where you need
out-of-band information to understand something, as we've just been
discussing in the threads about text handling - if you have a puddle
of bytes, you can't decode them to text without knowing what the
encoding is. [1] If your data's coming from JS, it won't be a
timedelta, it'll be a number; at some point you have to turn that into
a timedelta object, so you still have the same problem.
> Oh, and another thing I can do with a datetime that I can't do with a
> unix timestamp. I can represent the day I was born.
Maybe you can't with the original C definition of time_t as an
unsigned integer, but the notion of a Unix timestamp can plausibly be
extended (a) to negative numbers, and (b) to non-integers. Python
definitely does the latter; its ability to do the former depends
somewhat on the underlying C library's support:
Windows:
>>> time.strftime("%Y%m",time.gmtime(-100000))
Traceback (most recent call last):
File "<pyshell#163>", line 1, in <module>
time.strftime("%Y%m",time.gmtime(-100000))
OSError: [Errno 22] Invalid argument
Linux:
>>> time.strftime("%Y%m",time.gmtime(-100000))
'196912'
>>> time.strftime("%Y%m",time.gmtime(-2**31))
'190112'
>>> time.strftime("%Y%m",time.gmtime(-2**31-1))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: timestamp out of range for platform time_t
So what I'm seeing here is that the direct use of a time_t will cover
everything in an ugly way, but that a class wrapping it up could fix
that. And fundamentally, the only problem with datetime (which, for
the most part, is exactly that wrapper) is that it's unobvious how to
get a simple UTC timestamp.
Has the unobviousness been solved by a simple recipe? And if so,
should that tip be added to the datetime module docs somewhere?
ChrisA
[1] Yes, I said "puddle of bytes". What would you call it? Am
interested to hear!
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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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