- raise Exception for unsupported operations with duration and date/datetime objects

- store year and month as Decimal in Duration object.
- added test cases to support changes
closes #2

3 files changed, 29 insertions, 8 deletions

diff --git a/src/isodate/duration.py b/src/isodate/duration.py
index fa501cd..0d5e0fa 100644
--- a/src/isodate/duration.py
+++ b/src/isodate/duration.py
@@ -140,6 +140,8 @@ class Duration(object):
             newduration.tdelta = self.tdelta + other.tdelta
             return newduration
         if isinstance(other, (date, datetime)):
+            if (not( float(self.years).is_integer() and float(self.months).is_integer())):
+                raise ValueError('fractional years or months not supported for date calculations')
             newmonth = other.month + self.months
             carry, newmonth = fquotmod(newmonth, 1, 13)
             newyear = other.year + self.years + carry
@@ -162,6 +164,8 @@ class Duration(object):
             newduration.tdelta = self.tdelta + other
             return newduration
         if isinstance(other, (date, datetime)):
+            if (not( float(self.years).is_integer() and float(self.months).is_integer())):
+                raise ValueError('fractional years or months not supported for date calculations')
             newmonth = other.month + self.months
             carry, newmonth = fquotmod(newmonth, 1, 13)
             newyear = other.year + self.years + carry
@@ -199,6 +203,8 @@ class Duration(object):
         '''
         #print '__rsub__:', self, other
         if isinstance(other, (date, datetime)):
+            if (not( float(self.years).is_integer() and float(self.months).is_integer())):
+                raise ValueError('fractional years or months not supported for date calculations')
             newmonth = other.month - self.months
             carry, newmonth = fquotmod(newmonth, 1, 13)
             newyear = other.year - self.years + carry
diff --git a/src/isodate/isoduration.py b/src/isodate/isoduration.py
index 3554b1f..97affdc 100644
--- a/src/isodate/isoduration.py
+++ b/src/isodate/isoduration.py
@@ -31,6 +31,7 @@ It also provides a wrapper to strftime. This wrapper makes it easier to
 format timedelta or Duration instances as ISO conforming strings.
 '''
 from datetime import timedelta
+from decimal import Decimal
 import re
 
 from isodate.duration import Duration
@@ -103,7 +104,11 @@ def parse_duration(datestring):
             if val is None:
                 groups[key] = "0n"
             #print groups[key]
-            groups[key] = float(groups[key][:-1].replace(',', '.'))
+            if key in ('years', 'months'):
+                groups[key] = Decimal(groups[key][:-1].replace(',', '.'))
+            else:
+                # these values are passed into a timedelta object, which works with floats.
+                groups[key] = float(groups[key][:-1].replace(',', '.'))
     if groups["years"] == 0 and groups["months"] == 0:
         ret = timedelta(days=groups["days"], hours=groups["hours"],
                         minutes=groups["minutes"], seconds=groups["seconds"],
diff --git a/src/isodate/tests/test_duration.py b/src/isodate/tests/test_duration.py
index d8b4cf2..a66652e 100644
--- a/src/isodate/tests/test_duration.py
+++ b/src/isodate/tests/test_duration.py
@@ -192,12 +192,18 @@ DATE_CALC_TEST_CASES = (
                     (Duration(years=1, months=1, weeks=5),
                      date(2000, 1, 30),
                      date(2001, 4, 4)),
-                    (Duration(years=1, months=1, weeks=5),
-                     'raise exception',
-                     None),
-                    ('raise exception',
-                     Duration(years=1, months=1, weeks=5),
+                    (parse_duration("P1Y1M5W"),
+                     date(2000, 1, 30),
+                     date(2001, 4, 4)),
+                    (parse_duration("P0.5Y"),
+                     date(2000, 1, 30),
                      None),
+                    (Duration(years=1, months=1, hours=3),
+                     datetime(2000, 1, 30, 12, 15, 00),
+                     datetime(2001, 2, 28, 15, 15, 00)),
+                    (parse_duration("P1Y1MT3H"),
+                     datetime(2000, 1, 30, 12, 15, 00),
+                     datetime(2001, 2, 28, 15, 15, 00)),
                     (Duration(years=1, months=2),
                      timedelta(days=1),
                      Duration(years=1, months=2, days=1)),
@@ -239,7 +245,11 @@ class DurationTest(unittest.TestCase):
                           date(2000, 1, 1))
         self.assertRaises(TypeError, operator.sub, 'raise exc',
                           Duration(years=1))
-
+        self.assertRaises(TypeError, operator.add, Duration(years=1, months=1, weeks=5),
+                          'raise exception')
+        self.assertRaises(TypeError, operator.add, 'raise exception', 
+                          Duration(years=1, months=1, weeks=5))
+        
     def test_parseerror(self):
         '''
         Test for unparseable duration string.
@@ -451,7 +461,7 @@ def create_datecalctestcase(start, duration, expectation):
             Test operator +.
             '''
             if expectation is None:
-                self.assertRaises(TypeError, operator.add, start, duration)
+                self.assertRaises(ValueError, operator.add, start, duration)
             else:
                 self.assertEqual(start + duration, expectation)