BUG: offset normalize option may not work in addition/subtraction

doc/source/timeseries.rst

@@ -493,7 +493,7 @@ The basic ``DateOffset`` takes the same arguments as
 
 .. ipython:: python
 
-   d = datetime(2008, 8, 18)
+   d = datetime(2008, 8, 18, 9, 0)
    d + relativedelta(months=4, days=5)
 
 We could have done the same thing with ``DateOffset``:
@@ -568,10 +568,21 @@ particular day of the week:
 
 .. ipython:: python
 
+   d
    d + Week()
    d + Week(weekday=4)
    (d + Week(weekday=4)).weekday()
 
+   d - Week()
+
+``normalize`` option will be effective for addition and subtraction.
+
+.. ipython:: python
+
+   d + Week(normalize=True)
+   d - Week(normalize=True)
+
+
 Another example is parameterizing ``YearEnd`` with the specific ending month:
 
 .. ipython:: python

pandas/tseries/offsets.py

@@ -157,7 +157,7 @@ def isAnchored(self):
         return (self.n == 1)
 
     def copy(self):
-        return self.__class__(self.n, **self.kwds)
+        return self.__class__(self.n, normalize=self.normalize, **self.kwds)
 
     def _should_cache(self):
         return self.isAnchored() and self._cacheable
@@ -251,34 +251,34 @@ def __sub__(self, other):
         if isinstance(other, datetime):
             raise TypeError('Cannot subtract datetime from offset.')
         elif type(other) == type(self):
-            return self.__class__(self.n - other.n, **self.kwds)
+            return self.__class__(self.n - other.n, normalize=self.normalize, **self.kwds)
         else:  # pragma: no cover
             return NotImplemented
 
     def __rsub__(self, other):
-        return self.__class__(-self.n, **self.kwds) + other
+        return self.__class__(-self.n, normalize=self.normalize, **self.kwds) + other
 
     def __mul__(self, someInt):
-        return self.__class__(n=someInt * self.n, **self.kwds)
+        return self.__class__(n=someInt * self.n, normalize=self.normalize, **self.kwds)
 
     def __rmul__(self, someInt):
         return self.__mul__(someInt)
 
     def __neg__(self):
-        return self.__class__(-self.n, **self.kwds)
+        return self.__class__(-self.n, normalize=self.normalize, **self.kwds)
 
     @apply_wraps
     def rollback(self, dt):
         """Roll provided date backward to next offset only if not on offset"""
         if not self.onOffset(dt):
-            dt = dt - self.__class__(1, **self.kwds)
+            dt = dt - self.__class__(1, normalize=self.normalize, **self.kwds)
         return dt
 
     @apply_wraps
     def rollforward(self, dt):
         """Roll provided date forward to next offset only if not on offset"""
         if not self.onOffset(dt):
-            dt = dt + self.__class__(1, **self.kwds)
+            dt = dt + self.__class__(1, normalize=self.normalize, **self.kwds)
         return dt
 
     def onOffset(self, dt):

pandas/tseries/tests/test_offsets.py

@@ -361,6 +361,42 @@ def test_onOffset(self):
             date = datetime(dt.year, dt.month, dt.day)
             self.assert_(offset_n.onOffset(date))
 
+    def test_add(self):
+        dt = datetime(2011, 1, 1, 9, 0)
+
+        for offset in self.offset_types:
+            offset_s = self._get_offset(offset)
+            expected = self.expecteds[offset.__name__]
+
+            result_dt = dt + offset_s
+            result_ts = Timestamp(dt) + offset_s
+            for result in [result_dt, result_ts]:
+                self.assertTrue(isinstance(result, Timestamp))
+                self.assertEqual(result, expected)
+
+            tm._skip_if_no_pytz()
+            for tz in self.timezones:
+                expected_localize = expected.tz_localize(tz)
+                result = Timestamp(dt, tz=tz) + offset_s
+                self.assert_(isinstance(result, Timestamp))
+                self.assertEqual(result, expected_localize)
+
+            # normalize=True
+            offset_s = self._get_offset(offset, normalize=True)
+            expected = Timestamp(expected.date())
+
+            result_dt = dt + offset_s
+            result_ts = Timestamp(dt) + offset_s
+            for result in [result_dt, result_ts]:
+                self.assertTrue(isinstance(result, Timestamp))
+                self.assertEqual(result, expected)
+
+            for tz in self.timezones:
+                expected_localize = expected.tz_localize(tz)
+                result = Timestamp(dt, tz=tz) + offset_s
+                self.assert_(isinstance(result, Timestamp))
+                self.assertEqual(result, expected_localize)
+
 
 class TestDateOffset(Base):
     _multiprocess_can_split_ = True

pandas/tslib.pyx

@@ -753,7 +753,10 @@ cdef class _Timestamp(datetime):
 
         elif isinstance(other, timedelta) or hasattr(other, 'delta'):
             nanos = _delta_to_nanoseconds(other)
-            return Timestamp(self.value + nanos, tz=self.tzinfo, offset=self.offset)
+            result = Timestamp(self.value + nanos, tz=self.tzinfo, offset=self.offset)
+            if getattr(other, 'normalize', False):
+                result = Timestamp(normalize_date(result))
+            return result
 
         result = datetime.__add__(self, other)
         if isinstance(result, datetime):