BUG: DataFrame.reset_index loses timezone information

pandas/core/frame.py

@@ -35,6 +35,7 @@
 from pandas.util.decorators import deprecate, Appender, Substitution
 
 from pandas.tseries.period import PeriodIndex
+from pandas.tseries.index import DatetimeIndex
 
 import pandas.core.algorithms as algos
 import pandas.core.datetools as datetools
@@ -2813,6 +2814,9 @@ def _maybe_cast(values):
                     name = tuple(name_lst)
             if isinstance(self.index, PeriodIndex):
                 values = self.index.asobject
+            elif (isinstance(self.index, DatetimeIndex) and
+                  self.index.tz is not None):
+                values = self.index.asobject
             else:
                 values = self.index.values
             new_obj.insert(0, name, _maybe_cast(values))

pandas/tseries/tests/test_timezones.py

@@ -529,6 +529,14 @@ def test_frame_from_records_utc(self):
         # it works
         DataFrame.from_records([rec], index='begin_time')
 
+    def test_frame_reset_index(self):
+        dr = date_range('2012-06-02', periods=10, tz='US/Eastern')
+        df = DataFrame(np.random.randn(len(dr)), dr)
+        roundtripped = df.reset_index().set_index('index')
+        xp = df.index.tz
+        rs = roundtripped.index.tz
+        self.assertEquals(xp, rs)
+
     def test_dateutil_tzoffset_support(self):
         from dateutil.tz import tzoffset
         values = [188.5, 328.25]

vb_suite/timeseries.py

@@ -175,3 +175,19 @@ def date_range(start=None, end=None, periods=None, freq=None):
 datetimeindex_normalize = \
     Benchmark('rng.normalize()', setup,
               start_date=datetime(2012, 9, 1))
+
+setup = common_setup + """
+rng = date_range('1/1/2000', periods=100000, freq='H')
+df = DataFrame(np.random.randn(len(rng), 2), rng)
+"""
+
+dti_reset_index = \
+    Benchmark('df.reset_index()', setup, start_date=datetime(2012,9,1))
+
+setup = common_setup + """
+rng = date_range('1/1/2000', periods=100000, freq='H')
+df = DataFrame(np.random.randn(len(rng), 2), rng, tz='US/Eastern')
+"""
+
+dti_reset_index_tz = \
+    Benchmark('df.reset_index()', setup, start_date=datetime(2012,9,1))