[Numpy-discussion] Default unit for datetime/timedelta

[Pierre GM]

On Jun 8, 2011, at 11:05 PM, Mark Wiebe wrote:

> The NEP and current implementation of the datetime specifies microseconds as the default unit when constructing and converting to datetimes and timedeltas.

AFAIU, the default is [us] when otherwise unspecified.

> Here are some current behaviors that are inconsistent with the microsecond default, but consistent with the "generic time unit" idea:
> 
> >>> np.timedelta64(10, 's') + 10
> numpy.timedelta64(20,'s')

Here, the unit is defined: 's'

> >>> np.datetime64('2011-03-12') + 3
> numpy.datetime64('2011-03-15','D')

OK, here it is not. But the result makes sense... Up to a certain point. If you try to guess the unit from a date given as a string, what happens in case of ambiguities ? Or do you restrict an input string to be strictly ISO8601 to remove those ?

> I'd like to make 'M8' and 'm8' be datetime data types with generic time units instead of microseconds as they are currently. This would also allow the possibility of extending the behavior of detecting the unit from the input string as:
> 
> >>> np.datetime64('2011-03-12T13')
> numpy.datetime64('2011-03-12T13-0600','h')
> 
> to also work with arrays, which currently work like this:
> 
> >>> np.array(['2011-03-12T13', '2012'], dtype='M8')
> array(['2011-03-12T13:00:00.000000-0600', '2011-12-31T18:00:00.000000-0600'], dtype='datetime64[us]')

Why is the second one not '2012-01-01T00:00:00-0600' ?

Otherwise, I'm all for it.