potential solution for roundtrip issue with microseconds (issue #187)

Changelog

@@ -3,6 +3,10 @@ version 1.2.1 (not yet released)
  * num2date uses 'proleptic_gregorian' scheme when basedate is post-Gregorian but date is pre-Gregorian
    (issue #182).
  * fix 1.2.0 regression (date2num no longer works with numpy scalar array inputs, issue #185).
+ * Fix for issue #187 (have date2num round to the nearest second when within 1
+   microsecond).
+ * Fix for issue #189 (leap years calculated incorrectly for negative years in
+   proleptic_gregorian calendar).
 
 version 1.2.0 (release tag v1.2.0rel)
 =====================================

README.md

@@ -12,6 +12,8 @@ Time-handling functionality from netcdf4-python
 ## News
 For details on the latest updates, see the [Changelog](https://github.com/Unidata/cftime/blob/master/Changelog).
 
+??/??/2020: Version 1.2.1 released.  Fixes a couple of regressions introduced in 1.2.0. See Changelog for details.
+
 7/06/2020:  version 1.2.0 released. New microsecond accurate algorithm for date2num/num2date contributed by [spencerkclark](https://github.com/spencerkclark). Bugs fixed in masked array handling.
 
 5/12/2020:  version 1.1.3 released.  Add isoformat method for compatibility with python datetime (issue #152).

cftime/_cftime.pyx

@@ -53,7 +53,7 @@ cdef int32_t* days_per_month_array = [
 _rop_lookup = {Py_LT: '__gt__', Py_LE: '__ge__', Py_EQ: '__eq__',
                Py_GT: '__lt__', Py_GE: '__le__', Py_NE: '__ne__'}
 
-__version__ = '1.2.0'
+__version__ = '1.2.1'
 
 # Adapted from http://delete.me.uk/2005/03/iso8601.html
 # Note: This regex ensures that all ISO8601 timezone formats are accepted - but, due to legacy support for other timestrings, not all incorrect formats can be rejected.
@@ -353,16 +353,28 @@ _MAX_INT64 = np.iinfo("int64").max
 _MIN_INT64 = np.iinfo("int64").min
 
 
-def cast_to_int(num):
+def cast_to_int(num, units=None):
     if num.dtype.kind in "iu":
         return num
     else:
         if np.any(num < _MIN_INT64) or np.any(num > _MAX_INT64):
             raise OverflowError('time values outside range of 64 bit signed integers')
         if isinstance(num, np.ma.core.MaskedArray):
             int_num = np.ma.masked_array(np.rint(num), dtype=np.int64)
+            # use ceil instead of rint if 1 microsec less than a second
+            # or floor if 1 microsec greater than a second (issue #187)
+            if units not in microsec_units and units not in millisec_units:
+                int_num = np.ma.where(int_num%1000000 == 1, \
+                          np.ma.masked_array(np.floor(num),dtype=np.int64), int_num)
+                int_num = np.ma.where(int_num%1000000 == 999999, \
+                          np.ma.masked_array(np.ceil(num),dtype=np.int64), int_num)
         else:
             int_num = np.array(np.rint(num), dtype=np.int64)
+            if units not in microsec_units and units not in millisec_units:
+                int_num = np.where(int_num%1000000 == 1, \
+                          np.array(np.floor(num),dtype=np.int64), int_num)
+                int_num = np.where(int_num%1000000 == 999999, \
+                          np.array(np.ceil(num),dtype=np.int64), int_num)
         return int_num
 
 
@@ -483,7 +495,7 @@ def num2date(
     times = np.asanyarray(times)  # Allow list as input
     times = upcast_times(times)
     scaled_times = scale_times(times, factor)
-    scaled_times = cast_to_int(scaled_times)
+    scaled_times = cast_to_int(scaled_times,units=unit)
 
     # Through np.timedelta64, convert integers scaled to have units of
     # microseconds to datetime.timedelta objects, the timedelta type compatible
@@ -1494,9 +1506,9 @@ cdef _is_leap(int year, calendar):
     if calendar == 'proleptic_gregorian' or (calendar == 'standard' and year > 1581):
         if tyear % 4: # not divisible by 4
             leap = False
-        elif year % 100: # not divisible by 100
+        elif tyear % 100: # not divisible by 100
             leap = True
-        elif year % 400: # not divisible by 400
+        elif tyear % 400: # not divisible by 400
             leap = False
         else:
             leap = True

test/test_cftime.py

@@ -808,6 +808,18 @@ def test_tz_naive(self):
 # issue #185: date2num should work the numpy scalar array of dates (1.2.0 regression)
         dates = np.array(datetime(2010, 2, 2, 0, 0))
         assert (date2num(dates, units="hours since 2010-02-01 00:00:00") == 24.)
+# issue #187 - roundtrip near second boundary
+        dt1 = datetime(1810, 4, 24, 16, 15, 10)
+        units = 'days since -4713-01-01 12:00'
+        dt2 = num2date(date2num(dt1, units), units)
+        assert(dt1 == dt2)
+# issue #189 - leap years calculated incorrectly for negative years in proleptic_gregorian calendar
+        dt1 = datetime(2020, 4, 24, 16, 15, 10)
+        units = 'days since -4713-01-01 12:00'
+        cal = 'proleptic_gregorian'
+        dt2 = num2date(date2num(dt1, units, cal), units, cal)
+        assert(dt1 == dt2)
+
 
 class TestDate2index(unittest.TestCase):