BUG: PeriodIndex as DataFrame column should box to Periods #2243 #2281

pandas/core/frame.py

@@ -2022,6 +2022,8 @@ def _sanitize_column(self, key, value):
 
                 if not isinstance(value, np.ndarray):
                     value = com._asarray_tuplesafe(value)
+                elif isinstance(value, PeriodIndex):
+                    value = value.asobject
                 else:
                     value = value.copy()
         else:
@@ -2699,7 +2701,11 @@ def _maybe_cast(values):
                     lev_num = self.columns._get_level_number(col_level)
                     name_lst[lev_num] = name
                     name = tuple(name_lst)
-            new_obj.insert(0, name, _maybe_cast(self.index.values))
+            if isinstance(self.index, PeriodIndex):
+                values = self.index.asobject
+            else:
+                values = self.index.values
+            new_obj.insert(0, name, _maybe_cast(values))
 
         new_obj.index = new_index
         return new_obj

pandas/tseries/tests/test_period.py

@@ -15,7 +15,7 @@
 from pandas import Timestamp
 from pandas.tseries.frequencies import MONTHS, DAYS
 from pandas.tseries.period import Period, PeriodIndex, period_range
-from pandas.tseries.index import DatetimeIndex, date_range
+from pandas.tseries.index import DatetimeIndex, date_range, Index
 from pandas.tseries.tools import to_datetime
 import pandas.tseries.period as pmod
 
@@ -1300,6 +1300,19 @@ def test_as_frame_columns(self):
         ts = df['1/1/2000']
         assert_series_equal(ts, df.ix[:, 0])
 
+    def test_frame_setitem(self):
+        rng = period_range('1/1/2000', periods=5)
+        rng.name = 'index'
+        df = DataFrame(randn(5, 3), index=rng)
+
+        df['Index'] = rng
+        rs = Index(df['Index'])
+        self.assert_(rs.equals(rng))
+
+        rs = df.reset_index().set_index('index')
+        self.assert_(isinstance(rs.index, PeriodIndex))
+        self.assert_(rs.index.equals(rng))
+
     def test_nested_dict_frame_constructor(self):
         rng = period_range('1/1/2000', periods=5)
         df = DataFrame(randn(10, 5), columns=rng)