Further improvements to datetime roundtripping

.github/workflows/miniconda.yml

@@ -40,7 +40,9 @@ jobs:
       run: |
         conda create --name TEST python=${{ matrix.python-version }} --file requirements.txt --file requirements-dev.txt
         source activate TEST
-        CYTHON_COVERAGE=1 pip install -v -e  . --no-deps --force-reinstall
+        # enabling coverage slows down the tests dramaticaly
+        #CYTHON_COVERAGE=1 pip install -v -e  . --no-deps --force-reinstall
+        pip install -v -e  . --no-deps --force-reinstall
         conda info --all
         conda list
 

Changelog

@@ -1,3 +1,10 @@
+Unreleased
+==========
+* `cftime.date2num` will now always return an array of integers, if the units
+   and times allow.  Previously this would only be true if the units were
+   'microseconds' (PR #225).  In other circumstances, as before, `cftime.date2num`
+   will return an array of floats.
+
 version 1.3.1 (release tag v1.3.1rel)
 =====================================
  * fix for issue #211 (PR #212) bug in masked array handling in date2num)

src/cftime/_cftime.pyx

@@ -237,7 +237,7 @@ def date2num(dates,units,calendar=None):
         raise ValueError("Unsupported time units provided, {!r}.".format(unit))
     if unit in ["months", "month"] and calendar != "360_day":
         raise ValueError("Units of months only valid for 360_day calendar.")
-    factor = UNIT_CONVERSION_FACTORS[unit]
+    unit_timedelta = timedelta(microseconds=UNIT_CONVERSION_FACTORS[unit])
     can_use_python_basedatetime = _can_use_python_datetime(basedate,calendar)
 
     if can_use_python_basedatetime and all_python_datetimes:
@@ -263,13 +263,12 @@ def date2num(dates,units,calendar=None):
             times.append(None)
         else:
             td = date - basedate
-            if factor == 1.0:
-                # units are microseconds, use integer division
-                times.append(td // timedelta(microseconds=1) )
+            if td % unit_timedelta == timedelta(0):
+                # Explicitly cast result to np.int64 for Windows compatibility
+                quotient = np.int64(td // unit_timedelta)
+                times.append(quotient)
             else:
-                #times.append( (td / timedelta(microseconds=1)) / factor )
-                # this appears to be faster.
-                times.append( (td.total_seconds()*1.e6) / factor )
+                times.append(td / unit_timedelta)
         n += 1
     if ismasked: # convert to masked array if input was masked array
         times = np.array(times)

test/test_cftime.py

@@ -1888,5 +1888,46 @@ def test_num2date_integer_upcast_required():
     np.testing.assert_equal(result, expected)
 
 
+@pytest.mark.parametrize(
+    "encoding_units", 
+    ["microseconds", "milliseconds", "seconds", "minutes", "hours", "days"]
+)
+@pytest.mark.parametrize(
+    "freq",
+    [
+        timedelta(microseconds=1),
+        timedelta(microseconds=1000), 
+        timedelta(seconds=1), 
+        timedelta(minutes=1), 
+        timedelta(hours=1), 
+        timedelta(days=1)
+    ], 
+    ids=lambda x: f"{x!r}"
+)
+def test_date2num_num2date_roundtrip(encoding_units, freq, calendar):
+    date_type = _EXPECTED_DATE_TYPES[calendar]
+    lengthy_timedelta = timedelta(days=291000 * 360)
+    times = np.array(
+        [
+            date_type(1, 1, 1), 
+            date_type(1, 1, 1) + lengthy_timedelta, 
+            date_type(1, 1, 1) + lengthy_timedelta + freq
+        ]
+    )
+    units = f"{encoding_units} since 0001-01-01"
+    encoded = date2num(times, units=units, calendar=calendar)
+    decoded = num2date(encoded, units=units, calendar=calendar)
+    encoding_units_as_timedelta = timedelta(microseconds=UNIT_CONVERSION_FACTORS[encoding_units])
+
+    if freq >= encoding_units_as_timedelta:
+        assert encoded.dtype == np.int64
+        np.testing.assert_equal(decoded, times)
+    else:
+        assert encoded.dtype == np.float64
+        tolerance = timedelta(microseconds=2000)
+        meets_tolerance = np.abs(decoded - times) <= tolerance
+        assert np.all(meets_tolerance)
+
+
 if __name__ == '__main__':
     unittest.main()