[Python-Dev] proposal: add basic time type to the standardlibrary (original) (raw)

Stephan Richter srichter@cbu.edu
Sun, 10 Feb 2002 10:07:50 -0600

> * Intervals can be added or subtracted from themselves and the types > above. > DateInterval > TimeInterval > DateTimeInterval > TimeStampInterval

Intervals are a bad idea.

Why? They are the same as your Deltas. Interval is the more common term I think, therefore I chose it. Maybe having a Time/Date/DateTime{Interval} is too much and they should be really one. So you would have DateTimeInterval and TimeStampInterval for the same reasons I describe below.

On the other hand Java does not seem to implement intervals at all, which I think is a bad idea, since RDBs support it.

import DateTime DateTime.parseInterval('6 mins 3 secs') # DateTime.DateTimeInterval is the default 6 minutes 3 seconds DateTime.parseInterval('50 secs 3 millis', type=DateTime.TimeStampInterval) # returns ticks 50.003

I still think that many types are a good thing; it leaves the developer with choice. However the module should be smart and hide some of the choice from you, if you are a beginner. For example I imagine this to work:

import DateTime date = DateTime.parseDateTime('2.1.2001') type(date).name Date time = DateTime.parseDateTime('12:00:00') type(time).name Time datetime = DateTime.parseDateTime('2.1.2001 12:00:00') type(datetime).name DateTime

You really only need two types: one referencing fixed points in time and another one for storing the delta between two such fixed points. Everything else can be modeled on top of those two.

Well yes, but this is a reason why I have such a hard rime to get mxDateTime into Zope. Your module is well suited for certain tasks, but not everybody wants to use mxDateTime for Date/Time manipulation. So, saving components of a date is for some uses much better than saving ticks and vice versa. I also talked with Jim Fulton about it, and he agrees that there is a need for more than one Date/Time type. However it should be easy of course to convert between both, the Timestamp and the DateTime type.

Here are some more examples:

import DateTime date = DateTime.parseDateTime('2.1.2001') type(date).name Date stamp = DateTime.TimeStamp(date) type(stamp).name TimeStamp

BTW, something I do not want to support is:

import DateTime date = DateTime.DateTime('2.1.2001')

Since putting parsing into the object itself is a big mess, as we noticed in the Zope 2.x DateTime implementation. I think there should be only two ways to initialize a DateTime object, one of which I showed above, which is responsible of converting TimeStamps to DateTimes (mmh, maybe that should be a module function as well). The other one is:

import DateTime DateTime.DateTime(2001, 2, 3) February 3, 2001 DateTime.DateTime('2001', '02', '03') # Of course it also supports strings here February 3, 2001 DateTime.DateTime(2001, 2, 3, 12, 0) February 3, 2001 12:00:00 DateTime.DateTime(2001, hour=12) # missing pieces will be replaced by 1 or 0 January 1, 2001 12:00:00 DateTime.DateTime(year=2001, month=2, day=3, hour=1, minute=2, second=3, millisecond=4, timezone=-6) # max amount of arguments February 3, 2001 01:02:03.004 -06:00

Please have a look at mxDateTime. It has these two types and much of what you described in your notes.

I know mxDateTime very well and have even suggested before to make it the Zope DateTime module and even put it in the standard Python distribution. Here is the mail from the Zope-Coders list: http://lists.zope.org/pipermail/zope-coders/2001-October/000100.html. You can follow the thread to see some responses. Also, the list of notes was made from my experience working with mxDateTime, Zope DateTime and PostGreSQL Dates/Times. I know it was not complete, but it had some of the hotspots in it.

BTW, you wouldn't believe how complicated dealing with date and time really is... ah, yes, and don't even think of ever getting DST to work properly :-/

Oh, I have seen and fixed the Zope DateTime implementation plenty and I have thought of the problem for 2.5 years now. The problem is that the US starts to use the German "." notation (as mentioned in my original mail) and other issues, which make it much harder. That is the reason why I want to build an ultra-flexible parsing engine. So you can do things like:

import DateTime DateTime.parseDateTime('03/02/01', format=DateTime.ISO) February 1, 2003 DateTime.parseDateTime('03/02/01', format=DateTime.US) March 2, 2001 DateTime.parseDateTime('03.02.01', format=DateTime.US) March 2, 2001 DateTime.parseDateTime('03/02/01', format=DateTime.GERMAN) # just in case Europe/Germany goes insane as well. February 3, 2001

But by default:

DateTime.parseDateTime('03/02/01') March 2, 2001 DateTime.parseDateTime('03.02.01') February 3, 2001

Regards, Stephan

-- Stephan Richter CBU - Physics and Chemistry Student Web2k - Web Design/Development & Technical Project Management