Merge pull request #252 from spencerkclark/pickle-subclasses

Ensure subclass type is properly roundtripped during pickling

Changelog

@@ -2,6 +2,8 @@ version 1.5.1 (not yet released)
 ======================================
  * added support for "common_year" and "common_years" units for "noleap" 
    and "365_day" calendars (issue #5, PR #246)
+ * fixed a bug that led to subclasses losing their type identity upon
+   pickling (issue #251, PR #252).
 
 version 1.5.0 (release tag v1.5.0.rel)
 ======================================

src/cftime/_cftime.pyx

@@ -929,7 +929,7 @@ cdef _year_zero_defaults(calendar):
        return False
 
 # factory function without optional kwargs that can be used in datetime.__reduce__
-def _create_datetime(args, kwargs): return datetime(*args, **kwargs)
+def _create_datetime(date_type, args, kwargs): return date_type(*args, **kwargs)
 # custorm warning for invalid CF dates.
 class CFWarning(UserWarning):
     pass
@@ -1255,7 +1255,8 @@ The default format of the string produced by strftime is controlled by self.form
     def __reduce__(self):
         """special method that allows instance to be pickled"""
         args, kwargs = self._getstate()
-        return (_create_datetime, (args, kwargs))
+        date_type = type(self)
+        return (_create_datetime, (date_type, args, kwargs))
 
     cdef _add_timedelta(self, other):
         return NotImplemented

test/test_cftime.py

@@ -1305,8 +1305,15 @@ def test_pickling(self):
         import pickle
 
         date = Datetime360Day(year=1, month=2, day=3, hour=4, minute=5, second=6, microsecond=7)
-        self.assertEqual(date, pickle.loads(pickle.dumps(date)))
-
+        deserialized = pickle.loads(pickle.dumps(date))
+        self.assertEqual(date, deserialized)
+        self.assertEqual(type(date), type(deserialized))
+
+        date = datetimex(1, 2, 3, 4, 5, 6, 7, calendar="360_day")
+        deserialized = pickle.loads(pickle.dumps(date))
+        self.assertEqual(date, deserialized)
+        self.assertEqual(type(date), type(deserialized))
+
     def test_misc(self):
         "Miscellaneous tests."
         # make sure repr succeeds