From 74589df479dc6471ba18ec40b68260347c6dd049 Mon Sep 17 00:00:00 2001
From: Chang She <chang@lambdafoundry.com>
Date: Wed, 30 May 2012 00:45:55 -0400
Subject: [PATCH 1/2] BUG: raise exception on NaT in DatetimeIndex.astype('O')
 #1340

---
 pandas/tseries/index.py                 | 4 ++++
 pandas/tseries/tests/test_timeseries.py | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/pandas/tseries/index.py b/pandas/tseries/index.py
index 4fe9130c3a0d1..f760ac4faec5e 100644
--- a/pandas/tseries/index.py
+++ b/pandas/tseries/index.py
@@ -5,6 +5,7 @@
 
 import numpy as np
 
+from pandas.core.common import isnull
 from pandas.core.index import Index, Int64Index
 from pandas.tseries.frequencies import infer_freq, to_offset
 from pandas.tseries.offsets import DateOffset, generate_range, Tick
@@ -513,6 +514,9 @@ def astype(self, dtype):
         dtype = np.dtype(dtype)
 
         if dtype == np.object_:
+            if isnull(self).any():
+                msg = 'DatetimeIndex with NaT cannot be converted to object'
+                raise ValueError(msg)
             return self.asobject
         return Index.astype(self, dtype)
 
diff --git a/pandas/tseries/tests/test_timeseries.py b/pandas/tseries/tests/test_timeseries.py
index 9a0d6e6490942..ec572e2268f13 100644
--- a/pandas/tseries/tests/test_timeseries.py
+++ b/pandas/tseries/tests/test_timeseries.py
@@ -910,6 +910,10 @@ def test_index_conversion(self):
 
         self.assertRaises(ValueError, DatetimeIndex, ['a', 'b', 'c', 'd'])
 
+    def test_object_convert_fail(self):
+        idx = DatetimeIndex([NaT])
+        self.assertRaises(ValueError, idx.astype, 'O')
+
     def test_setops_conversion_fail(self):
         index = self.frame.index
 

From 956c8147208a1d9e894635033b0eaf11b102c928 Mon Sep 17 00:00:00 2001
From: Chang She <chang@lambdafoundry.com>
Date: Thu, 31 May 2012 23:23:53 -0400
Subject: [PATCH 2/2] push exception down to asobject

---
 pandas/tseries/index.py | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/pandas/tseries/index.py b/pandas/tseries/index.py
index f760ac4faec5e..e1b033eb88227 100644
--- a/pandas/tseries/index.py
+++ b/pandas/tseries/index.py
@@ -514,9 +514,6 @@ def astype(self, dtype):
         dtype = np.dtype(dtype)
 
         if dtype == np.object_:
-            if isnull(self).any():
-                msg = 'DatetimeIndex with NaT cannot be converted to object'
-                raise ValueError(msg)
             return self.asobject
         return Index.astype(self, dtype)
 
@@ -536,6 +533,12 @@ def asobject(self):
         """
         Convert to Index of datetime objects
         """
+        if isnull(self).any():
+            msg = 'DatetimeIndex with NaT cannot be converted to object'
+            raise ValueError(msg)
+        return self._get_object_index()
+
+    def _get_object_index(self):
         boxed_values = _dt_box_array(self.asi8, self.offset, self.tz)
         return Index(boxed_values, dtype=object)
 
@@ -1013,7 +1016,7 @@ def normalize(self):
         return DatetimeIndex(new_values, freq='infer', name=self.name)
 
     def __iter__(self):
-        return iter(self.asobject)
+        return iter(self._get_object_index())
 
     def searchsorted(self, key, side='left'):
         if isinstance(key, np.ndarray):