[Numpy-discussion] code review/build & test for datetime business day API

Derek Homeier derek@astro.physik.uni-goettingen...
Thu Jun 16 17:52:19 CDT 2011

Hi Mark,

On 16.06.2011, at 5:40PM, Mark Wiebe wrote:

>> >>> np.datetime64('2011-06-16 02:03:04Z', 'D')
>> np.datetime64('0000-06-16','D')
>> I've tried to track this down in datetime.c, but unsuccessfully so (i.e. I could not connect it
>> to any of the dts->year assignments therein).
> This is definitely perplexing. Probably the first thing to check is whether it's breaking during parsing or printing. This should always produce the same result:
> >>> np.datetime64('1970-03-23 20:00:00Z').astype('i8')
> 7070400
> But maybe the test_days_creation is already checking that thoroughly enough.
> Then, maybe printf-ing the year value at various stages of the printing, like in set_datetimestruct_days, after convert_datetime_to_datetimestruct, and in make_iso_8601_date. This would at least isolate where the year is getting lost.
ok, that was a lengthy hunt, but it's in printing the string in make_iso_8601_date:

    tmplen = snprintf(substr, sublen, "%04" NPY_INT64_FMT, dts->year);
    fprintf(stderr, "printed %d[%d]: dts->year=%lld: %s\n", tmplen, sublen, dts->year, substr);


>>> np.datetime64('1970-03-23 20:00:00Z', 'D')
printed 4[62]: dts->year=1970: 0000

It seems snprintf is not using the correct format for INT64 (as I happened to do in fprintf before 
realising I had to use "%lld" ;-) - could it be this is a general issue, which just does not show up 
on little-endian machines because they happen to pass the right half of the int64 to printf?
BTW, how is this supposed to be handled (in 4 digits) if the year is indeed beyond the 32bit range 
(i.e. >~ 0.3 Hubble times...)? Just wondering if one could simply cast it to int32 before print.


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