Convert np.datetime64 to pydatetime

src/cftime/_cftime.pyx

@@ -209,6 +209,11 @@ def date2num(dates, units, calendar=None, has_year_zero=None, longdouble=False):
         mask = dates.mask
         ismasked = True
 
+    # Convert numpy.datetime64 to a list to convert them to datetime instances.
+    if hasattr(dates, "dtype"):
+        if np.issubdtype(dates.dtype, np.datetime64):
+            dates = dates.tolist()
+
     # are all input dates 'real' python datetime objects?
     dates = np.asanyarray(dates) # convert to numpy array
     shape = dates.shape # save shape of input

test/test_cftime.py

@@ -2170,6 +2170,22 @@ def test_date2num_missing_data():
     assert out is np.ma.masked
 
 
+def test_date2num_numpy_datetime64():
+    # Array
+    array = np.array([
+        np.datetime64(123, "s"),
+        np.datetime64(124, "s"),
+        np.datetime64(125, "s")
+    ])
+    out = date2num(array, units="seconds since 1970-01-01T00:00:00", calendar="gregorian")
+    assert ((out == np.array([123, 124, 125]))).all()
+
+    # Scalar
+    array = np.datetime64(123, "s")
+    out = date2num(array, units="seconds since 1970-01-01T00:00:00", calendar="gregorian")
+    assert out == np.int64(123)
+
+
 def test_num2date_preserves_shape():
     # The optimized num2date algorithm operates on a flattened array.  This
     # check ensures that the original shape of the times is restored in the