BUG: don't lose tzinfo when shifting by different frequency close pandas-dev#1683

Author: wesm

RELEASE.rst

@@ -64,6 +64,7 @@ pandas 0.8.2
   - Fix errors with how='median' and generic NumPy resampling in some cases
     caused by SeriesBinGrouper (#1648, #1688)
   - When grouping by level, exclude unobserved levels (#1697)
+  - Don't lose tzinfo in DatetimeIndex when shifting by different offset (#1683)
 
 pandas 0.8.1
 ============

pandas/tseries/index.py

@@ -656,7 +656,10 @@ def shift(self, n, freq=None):
         if freq is not None and freq != self.offset:
             if isinstance(freq, basestring):
                 freq = to_offset(freq)
-            return Index.shift(self, n, freq)
+            result = Index.shift(self, n, freq)
+            result.tz = self.tz
+
+            return result
 
         if n == 0:
             # immutable so OK
@@ -668,7 +671,7 @@ def shift(self, n, freq=None):
         start = self[0] + n * self.offset
         end = self[-1] + n * self.offset
         return DatetimeIndex(start=start, end=end, freq=self.offset,
-                             name=self.name)
+                             name=self.name, tz=self.tz)
 
     def repeat(self, repeats, axis=None):
         """

pandas/tseries/tests/test_timezones.py

@@ -397,6 +397,14 @@ def test_tz_convert_unsorted(self):
         exp = dr.hour[::-1]
         tm.assert_almost_equal(result, exp)
 
+    def test_shift_localized(self):
+        dr = date_range('2011/1/1', '2012/1/1', freq='W-FRI')
+        dr_tz = dr.tz_localize('US/Eastern')
+
+        result = dr_tz.shift(1, '10T')
+        self.assert_(result.tz == dr_tz.tz)
+
+
 class TestTimeZones(unittest.TestCase):
 
     def setUp(self):