Bug in strftime(): "unsupported calendar"

[davidhassell]

Hello,

I think I found a bug (or feature?) in strftime, that was introduced in 1.1.2 and is causing failures in my code:

All is well at 1.1.1.2:

In [1]: import cftime                                                                                       

In [2]: cftime.__version__                                                                                  
Out[2]: '1.1.1.2'

In [3]: c = cftime.datetime(*cftime._parse_date('7480-01-01 00:00:00')) 

In [4]: c.strftime()                                                                                        
Out[4]: '7480-01-01 00:00:00'

In [5]: c.calendar                                                               
Out[5]: ''

But not at 1.1.2

In [8]: import cftime

In [9]: cftime.__version__
Out[9]: '1.1.2'

In [10]: c = cftime.datetime(*cftime._parse_date('7480-01-01 00:00:00'))

In [11]: c.strftime()
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-11-a934a194dce4> in <module>()
----> 1 c.strftime()

cftime/_cftime.pyx in cftime._cftime.datetime.strftime()

cftime/_cftime.pyx in cftime._cftime._strftime()

cftime/_cftime.pyx in cftime._cftime.datetime.timetuple()

cftime/_cftime.pyx in cftime._cftime.datetime.dayofyr.__get__()

cftime/_cftime.pyx in cftime._cftime.JulianDayFromDate()

cftime/_cftime.pyx in cftime._cftime._IntJulianDayFromDate()

cftime/_cftime.pyx in cftime._cftime._check_calendar()

ValueError: unsupported calendar

In [12]: 

In [13]: c.calendar                                                               
Out[5]: ''

I know that '' is not a valid calendar, but this worked as I expected in the previous version.

As this relates to the recent work that went into 1.1.2, I thought I'd raise it here first before suggesting a fix, but I am happy to investigate further if that helps.

Many thanks,
David

[jswhit2]

This seems to be related to the change that made dayofyr a property instead of an attribute. Since that calculation requires a calendar I don't see an obvious simple fix.

[jswhit2]

I guess one solution would be to make the default cftime.datetime calendar proleptic_gregorian (or standard) instead of an empty string.

[jswhit]

Fix in PR #170

[davidhassell]

That sounds like a good solution - thanks for the quick fix! I think I'd prefer standard, though, rather than proleptic_gregorian, as that is the CF conventions default calendar. Is that OK?

[jswhit]

The reason I went with proleptic_gregorian was so that cftime.datetime instances would behave like python datetime instances by default. However, I see why you would prefer standard since it's the most commonly used netcdf calendar.

[jswhit]

Changed it to standard, since that's the default calendar for everything else.

[davidhassell]

Thanks - that's good for me.

[jswhit]

PR #170 merged. I will push out a 1.1.3 release soon, since this is a pretty significant bug.