[Python-Dev] proposal: add basic time type to the standard library

[M.-A. Lemburg]

Jim Fulton wrote:
> 
> "M.-A. Lemburg" wrote:
> >
> > Jim Fulton wrote:
> ...
> 
> > > What is data roundtrip safety?
> >
> > Roundtrip safety means that e.g. if you take a COM date value
> > from a ADO and create a DateTime object with it, you can
> > be sure to get back the exact same value via the COMDate()
> > method.
> 
> Since I don't know what COMDate is, this doesn't mean
> anything to me. :)

Then you're lucky -- COMDates are just about the strangest
beast I've ever seen as date/time encoding.
 
> ...
> > I suppose that I could easily make a few calculation
> > lazy to enhance speed; memory footprint would not change
> > though. It's currently at 56 bytes per DateTime object
> > and 36 bytes per DateTimeDelta object.
> 
> Does that include the two words of Python object overhead?

I suppose so -- the values I quoted are the tp_size
values of the types. The instance will probably also require
a dictionary and the weak ref list on top of those figures.
 
> > To get similar accuracy in Python,
> 
> I assume you mean precision.

Eh, yes.
 
> > you'd need a float and
> > an integer per object,
> 
> It depends on the desired precision. To get minute
> precision, an int will do. Two ints can get you about
> a hundreth of a microsecond precision, which is more than
> most people need.

I was just trying to compare apples to apples :-)

mxDateTime offers the same precision as a float (for daytime) 
and an integer (for the day) can give.
 
> > that's 16 bytes + 12 bytes == 28 bytes
> > + malloc() overhead for the two and the wrapping instance
> > which gives another 32 bytes (provided you store the two
> > objects in slots)... >60 bytes per Python based date time
> > object.
> 
> A Python-based date-time object isn't very interesting to me.

You should have mentioned that earlier ;-)

-- 
Marc-Andre Lemburg
CEO eGenix.com Software GmbH
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