BUG: DatetimeIndex.join tz-aware issue with how='outer'. close #2317

RELEASE.rst

@@ -59,6 +59,8 @@ pandas 0.10.0
   - Raise exception on calling reset_index on Series with inplace=True (#2277)
   - Enable setting multiple columns in DataFrame with hierarchical columns
     (#2295)
+  - Respect dtype=object in DataFrame constructor (#2291)
+  - Fix DatetimeIndex.join bug with tz-aware indexes and how='outer' (#2317)
 
 pandas 0.9.1
 ============

pandas/tseries/index.py

@@ -869,7 +869,7 @@ def _wrap_joined_index(self, joined, other):
             return joined
         else:
             tz = getattr(other, 'tz', None)
-            return DatetimeIndex(joined, name=name, tz=tz)
+            return self._simple_new(joined, name, tz=tz)
 
     def _can_fast_union(self, other):
         if not isinstance(other, DatetimeIndex):

pandas/tseries/tests/test_timezones.py

@@ -622,7 +622,7 @@ def test_join_utc_convert(self):
             self.assert_(isinstance(result, DatetimeIndex))
             self.assert_(result.tz.zone == 'UTC')
 
-    def test_join_naive_with_aware(self):
+    def test_join_aware(self):
         rng = date_range('1/1/2011', periods=10, freq='H')
         ts = Series(np.random.randn(len(rng)), index=rng)
 
@@ -631,6 +631,20 @@ def test_join_naive_with_aware(self):
         self.assertRaises(Exception, ts.__add__, ts_utc)
         self.assertRaises(Exception, ts_utc.__add__, ts)
 
+        test1 = DataFrame(np.zeros((6,3)),
+                          index=date_range("2012-11-15 00:00:00", periods=6,
+                                           freq="100L", tz="US/Central"))
+        test2 = DataFrame(np.zeros((3,3)),
+                          index=date_range("2012-11-15 00:00:00", periods=3,
+                                           freq="250L", tz="US/Central"),
+                          columns=range(3,6))
+
+        result = test1.join(test2, how='outer')
+        ex_index = test1.index.union(test2.index)
+
+        self.assertTrue(result.index.equals(ex_index))
+        self.assertTrue(result.index.tz.zone == 'US/Central')
+
     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')