issue_comments: 241033630

I tried to look into the logic of decoding datetimes and I am not sure I got it. So the dtype of the dates should be:

if 1678 < year < 2262: `datetime64[ns]` else: if calendar in ['standard', 'gregorian', 'proleptic_gregorian']: `datetime.datetime` else: `netcdftime._datetime.datetime`

(Is it ever a timedelta64[ns]?)

The necessary conversion seems to be determined lazily (which may be the core of my problem above), Try this:

``` import xarray as xr import numpy as np

units = 'days since 1850-01-01 00:00:00' dates = np.arange(850) * 365

dta = xr.conventions.DecodedCFDatetimeArray(dates, units)

dta[0:1] # a datetime64[ns] object dta[-1] # a datetime.datetime object dta[:] # a datetime.datetime object ```

However, when I load these dates from a netCDF file (see the example in the first post) it results in an error. (Thus, the behavior is not exactly the same as when using DecodedCFDatetimeArray, I haven't figured out why.)

Another (or the same) problem is that in DecodedCFDatetimeArray in (in __init__) only the first element is tested when trying to generate the error message, maybe the first and the last element should be tested.

Here: (https://github.com/pydata/xarray/blob/master/xarray/conventions.py, line 375)