Merge pull request #586 from ckhroulev/issue-584

360_day and 365_day calendars: support negative Julian days. See #584.

Author: Jeff Whitaker

Changelog

@@ -5,6 +5,8 @@
  * Use valid_min/valid_max/valid_range attributes when defining mask
    (issue #576).  Values outside the valid range are considered to
    be missing when defining the mask.
+ * Fix for issue #584 (add support for dates before -4712-1-1 in 360_day
+   and 365_day calendars to netcdftime.utime).
 
  version 1.2.4 (tag v1.2.4rel)
 ==============================

netcdftime/netcdftime.py

@@ -393,7 +393,10 @@ def _DateFromNoLeapDay(JD):
     # based on redate.py by David Finlayson.
 
     if JD < 0:
-        raise ValueError('Julian Day must be positive')
+        year_offset = int(-JD) // 365 + 1
+        JD += year_offset * 365
+    else:
+        year_offset = 0
 
     dayofwk = int(math.fmod(int(JD + 1.5), 7))
     (F, Z) = math.modf(JD + 0.5)
@@ -428,7 +431,17 @@ def _DateFromNoLeapDay(JD):
     (sfrac, seconds) = math.modf(mfrac * 60.0)
     microseconds = sfrac*1.e6
 
-    return datetime(year, month, int(days), int(hours), int(minutes),
+    if year_offset > 0:
+        # correct dayofwk
+
+        # 365 mod 7 = 1, so the day of the week changes by one day for
+        # every year in year_offset
+        dayofwk -= int(math.fmod(year_offset, 7))
+
+        if dayofwk < 0:
+            dayofwk += 7
+
+    return datetime(year - year_offset, month, int(days), int(hours), int(minutes),
             int(seconds), int(microseconds),dayofwk, dayofyr)
 
 
@@ -495,7 +508,10 @@ def _DateFrom360Day(JD):
     """
 
     if JD < 0:
-        raise ValueError('Julian Day must be positive')
+        year_offset = int(-JD) // 360 + 1
+        JD += year_offset * 360
+    else:
+        year_offset = 0
 
     #jd = int(360. * (year + 4716)) + int(30. * (month - 1)) + day
     (F, Z) = math.modf(JD)
@@ -511,7 +527,7 @@ def _DateFrom360Day(JD):
     (sfrac, seconds) = math.modf(mfrac * 60.0)
     microseconds = sfrac*1.e6
 
-    return datetime(year, month, int(days), int(hours), int(minutes),
+    return datetime(year - year_offset, month, int(days), int(hours), int(minutes),
             int(seconds), int(microseconds), -1, dayofyr)
 
 

test/tst_netcdftime.py

@@ -659,5 +659,45 @@ def test_issue444(self):
         assert(index == 11)
         f.close()
 
+class issue584TestCase(unittest.TestCase):
+    """Regression tests for issue #584."""
+    converters = None
+
+    def setUp(self):
+        self.converters = {"360_day" : utime("days since 1-1-1", "360_day"),
+                           "365_day" : utime("days since 1-1-1", "365_day")}
+
+    def test_roundtrip(self):
+        "Test roundtrip conversion (num2date <-> date2num) using 360_day and 365_day calendars."
+
+        # Pick a date and time outside of the range of the Julian calendar.
+        date = datetimex(-5000, 1, 1, 12)
+
+        for calendar in ["360_day", "365_day"]:
+            converter = self.converters[calendar]
+            self.assertEqual(date, converter.num2date(converter.date2num(date)))
+
+    def test_dayofwk(self):
+        "Test computation of dayofwk in the 365_day calendar."
+
+        converter = self.converters["365_day"]
+
+        # Pick the date corresponding to the Julian day of 1.0 to test
+        # the transision from positive to negative Julian days.
+        julian_day = converter.date2num(datetimex(-4712, 1, 2, 12))
+
+        old_date = converter.num2date(julian_day)
+        for delta_year in range(1, 101): # 100 years cover several 7-year cycles
+            date = converter.num2date(julian_day - delta_year * 365)
+
+            # test that the day of the week changes by one every year (except
+            # for wrapping around every 7 years, of course)
+            if date.dayofwk == 6:
+                self.assertEqual(old_date.dayofwk, 0)
+            else:
+                self.assertEqual(old_date.dayofwk - date.dayofwk, 1)
+
+            old_date = date
+
 if __name__ == '__main__':
     unittest.main()