Unpin cftime

[bjlittle]

The cftime package has been pinned to 1.1.3 as the lastest offering 1.2.0 is causing epoch unit test failures, see #3750

We require to investigate and unpin asap. Either:

• Fix iris, or
• Raise an issue with the cftime developers

[stephenworsley]

It looks like num2date is giving a different value for certain dates when running this code:

import cftime
import cf_units
year = 1
hrs_unit = cf_units.Unit(("hours since epoch", calendar=cf_units.CALENDAR_GREGORIAN)
hrs_unit.date2num(cftime.datetime(year,1,1))

From experiments, it seems that there is a discrepancy between versions when year is between 1 and 1582 and there is no longer a discrepancy for year = 1583. For what its worth, 1582 is when the Gregorian calendar was first adopted. I wonder if there is some conversion going on for pre-Gregorian dates.

[stephenworsley]

It looks like cftime has just released version 1.2.1 which ought to include a fix for this.