Merge branch 'master' of https://github.com/pandas-dev/pandas into dt…

…arrays3

pandas/core/arrays/datetimes.py

@@ -100,4 +100,4 @@ def _sub_datelike_dti(self, other):
         if self.hasnans or other.hasnans:
             mask = (self._isnan) | (other._isnan)
             new_values[mask] = iNaT
-        return new_values.view('i8')
+        return new_values.view('timedelta64[ns]')

pandas/core/indexes/datetimelike.py

@@ -574,6 +574,28 @@ def _convert_scalar_indexer(self, key, kind=None):
         return (super(DatetimeIndexOpsMixin, self)
                 ._convert_scalar_indexer(key, kind=kind))
 
+    def _add_nat(self):
+        """Add pd.NaT to self"""
+        if is_period_dtype(self):
+            raise TypeError('Cannot add {cls} and {typ}'
+                            .format(cls=type(self).__name__,
+                                    typ=type(NaT).__name__))
+
+        # GH#19124 pd.NaT is treated like a timedelta for both timedelta
+        # and datetime dtypes
+        return self._nat_new(box=True)
+
+    def _sub_nat(self):
+        """Subtract pd.NaT from self"""
+        # GH#19124 Timedelta - datetime is not in general well-defined.
+        # We make an exception for pd.NaT, which in this case quacks
+        # like a timedelta.
+        # For datetime64 dtypes by convention we treat NaT as a datetime, so
+        # this subtraction returns a timedelta64 dtype.
+        # For period dtype, timedelta64 is a close-enough return dtype.
+        result = self._nat_new(box=False)
+        return result.view('timedelta64[ns]')
+
     def _addsub_offset_array(self, other, op):
         """
         Add or subtract array-like of DateOffset objects

pandas/core/indexes/period.py

@@ -22,9 +22,7 @@
 import pandas.tseries.frequencies as frequencies
 from pandas.tseries.frequencies import get_freq_code as _gfc
 from pandas.core.indexes.datetimes import DatetimeIndex, Int64Index, Index
-from pandas.core.indexes.timedeltas import TimedeltaIndex
-from pandas.core.indexes.datetimelike import (
-    DatelikeOps, DatetimeIndexOpsMixin)
+from pandas.core.indexes.datetimelike import DatelikeOps, DatetimeIndexOpsMixin
 from pandas.core.tools.datetimes import parse_time_string
 import pandas.tseries.offsets as offsets