Raise error upon construction of out-of-bounds datetime?

[spencerkclark]

In pydata/xarray#1252 I am working on a NetCDFTimeIndex that is intended to bring some of the features of pandas's DatetimeIndex (for now namely field accessors and partial datetime string indexing) to time indexes that use netcdftime._netcdftime.datetime objects.

Currently one can construct non-sensical datetimes using netcdftime._netcdftime.datetime objects:

In [1]: from netcdftime import DatetimeNoLeap

In [2]: DatetimeNoLeap(1, 45, 45)
Out[2]: netcdftime._netcdftime.DatetimeNoLeap(1, 45, 45, 0, 0, 0, 0, -1, 1)

Would it be possible for this kind of expression to raise an error? This would be nice, because that way if one tries to index with a slice involving an out-of-bounds datetime, it would automatically cause an error, rather than behave in the fashion below:

In [1]: import xarray as xr

In [2]: from xarray.conventions.netcdftimeindex import NetCDFTimeIndex

In [3]: from netcdftime import DatetimeNoLeap

In [4]: dates = [DatetimeNoLeap(1, 1, 1), DatetimeNoLeap(1, 2, 1), DatetimeNoLeap(2, 1, 1), DatetimeNoLeap(2, 2, 1)]

In [5]: da = xr.DataArray([1, 2, 3, 4], coords=[NetCDFTimeIndex(dates)], dims=['time'])

In [6]: da.sel(time=slice(DatetimeNoLeap(1, 1, 1), DatetimeNoLeap(1, 45, 45)))
Out[6]:
<xarray.DataArray (time: 2)>
array([1, 2])
Coordinates:
  * time     (time) object    1-01-01 00:00:00    1-02-01 00:00:00

cc @shoyer

[jhamman]

This should absolutely be done. We should be able to provide similar checks to what is provided in the datetime module.

In [1]: import datetime

In [2]: datetime.datetime(2000, 1, 45, -4)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-2492d881556f> in <module>()
----> 1 datetime.datetime(2000, 1, 45, -4)

ValueError: day is out of range for month

[jhamman]

closed via #12