Modify _encode_datetime_with_cftime for compatibility with cftime > 1.4.0 (#4871)

Author: spencerkclark

doc/whats-new.rst

@@ -96,6 +96,8 @@ Bug fixes
   :py:meth:`Dataset.to_zarr` (:issue:`4783`, :pull:`4795`).
   By `Julien Seguinot <https://github.com/juseg>`_.
 - Add :py:meth:`Dataset.drop_isel` and :py:meth:`DataArray.drop_isel` (:issue:`4658`, :pull:`4819`). By `Daniel Mesejo <https://github.com/mesejo>`_.
+- Fix time encoding bug associated with using cftime versions greater than
+  1.4.0 with xarray (:issue:`4870`, :pull:`4871`). By `Spencer Clark <https://github.com/spencerkclark>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/coding/times.py

@@ -391,7 +391,7 @@ def _encode_datetime_with_cftime(dates, units, calendar):
     def encode_datetime(d):
         return np.nan if d is None else cftime.date2num(d, units, calendar)
 
-    return np.vectorize(encode_datetime)(dates)
+    return np.array([encode_datetime(d) for d in dates.ravel()]).reshape(dates.shape)
 
 
 def cast_to_int_if_safe(num):

xarray/tests/test_coding_times.py

@@ -8,6 +8,7 @@
 
 from xarray import DataArray, Dataset, Variable, coding, conventions, decode_cf
 from xarray.coding.times import (
+    _encode_datetime_with_cftime,
     cftime_to_nptime,
     decode_cf_datetime,
     encode_cf_datetime,
@@ -995,3 +996,18 @@ def test_encode_decode_roundtrip(freq):
     encoded = conventions.encode_cf_variable(variable)
     decoded = conventions.decode_cf_variable("time", encoded)
     assert_equal(variable, decoded)
+
+
+@requires_cftime
+def test__encode_datetime_with_cftime():
+    # See GH 4870. cftime versions > 1.4.0 required us to adapt the
+    # way _encode_datetime_with_cftime was written.
+    import cftime
+
+    calendar = "gregorian"
+    times = cftime.num2date([0, 1], "hours since 2000-01-01", calendar)
+
+    encoding_units = "days since 2000-01-01"
+    expected = cftime.date2num(times, encoding_units, calendar)
+    result = _encode_datetime_with_cftime(times, encoding_units, calendar)
+    np.testing.assert_equal(result, expected)