BUG: align two tz aware frames loses tz #2127

Author: changhiskhan

pandas/tseries/index.py

@@ -864,7 +864,8 @@ def _wrap_joined_index(self, joined, other):
             joined.name = name
             return joined
         else:
-            return DatetimeIndex(joined, name=name)
+            tz = getattr(other, 'tz', None)
+            return DatetimeIndex(joined, name=name, tz=tz)
 
     def _can_fast_union(self, other):
         if not isinstance(other, DatetimeIndex):

pandas/tseries/tests/test_timezones.py

@@ -621,6 +621,15 @@ def test_join_naive_with_aware(self):
         self.assertRaises(Exception, ts.__add__, ts_utc)
         self.assertRaises(Exception, ts_utc.__add__, ts)
 
+    def test_align_aware(self):
+        idx1 = date_range('2001', periods=5, freq='H', tz='US/Eastern')
+        idx2 = date_range('2001', periods=5, freq='2H', tz='US/Eastern')
+        df1 = DataFrame(np.random.randn(len(idx1), 3), idx1)
+        df2 = DataFrame(np.random.randn(len(idx2), 3), idx2)
+        new1, new2 = df1.align(df2)
+        self.assertEqual(df1.index.tz, new1.index.tz)
+        self.assertEqual(df2.index.tz, new2.index.tz)
+
     def test_equal_join_ensure_utc(self):
         rng = date_range('1/1/2011', periods=10, freq='H', tz='US/Eastern')
         ts = Series(np.random.randn(len(rng)), index=rng)