BUG: fix time zone handling in union between non-overlapping DatetimeIndex. close #2367

Author: wesm

RELEASE.rst

@@ -77,6 +77,8 @@ pandas 0.10.0
     something weird) (#2263)
   - Prevent uint64 -> int64 overflows (#2355)
   - Enable joins between MultiIndex and regular Index (#2024)
+  - Fix time zone metadata issue when unioning non-overlapping DatetimeIndex
+    objects (#2367)
 
 pandas 0.9.1
 ============

pandas/tseries/index.py

@@ -824,7 +824,7 @@ def union(self, other):
         else:
             result = Index.union(this, other)
             if isinstance(result, DatetimeIndex):
-                result.tz = self.tz
+                result.tz = this.tz
                 if result.freq is None:
                     result.offset = to_offset(result.inferred_freq)
             return result

pandas/tseries/tests/test_timezones.py

@@ -645,6 +645,16 @@ def test_join_aware(self):
         self.assertTrue(result.index.equals(ex_index))
         self.assertTrue(result.index.tz.zone == 'US/Central')
 
+        # non-overlapping
+        rng = date_range("2012-11-15 00:00:00", periods=6,
+                         freq="H", tz="US/Central")
+
+        rng2 = date_range("2012-11-15 12:00:00", periods=6,
+                         freq="H", tz="US/Eastern")
+
+        result = rng.union(rng2)
+        self.assertTrue(result.tz.zone == 'UTC')
+
     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')