Change default to str

This makes the default na repr match the expected type
for the formatter.

pandas/core/arrays/datetimelike.py

@@ -317,7 +317,7 @@ def _ndarray_values(self):
     # ----------------------------------------------------------------
     # Rendering Methods
 
-    def _format_native_types(self, na_rep=u'NaT', date_format=None):
+    def _format_native_types(self, na_rep='NaT', date_format=None):
         """
         Helper method for astype when converting to strings.
 

pandas/core/arrays/datetimes.py

@@ -525,7 +525,7 @@ def _validate_fill_value(self, fill_value):
     # -----------------------------------------------------------------
     # Rendering Methods
 
-    def _format_native_types(self, na_rep=u'NaT', date_format=None, **kwargs):
+    def _format_native_types(self, na_rep='NaT', date_format=None, **kwargs):
         from pandas.io.formats.format import _get_format_datetime64_from_values
         fmt = _get_format_datetime64_from_values(self, date_format)
 

pandas/core/arrays/period.py

@@ -572,7 +572,7 @@ def asfreq(self, freq=None, how='E'):
     # ------------------------------------------------------------------
     # Rendering Methods
 
-    def _format_native_types(self, na_rep=u'NaT', date_format=None, **kwargs):
+    def _format_native_types(self, na_rep='NaT', date_format=None, **kwargs):
         """
         actually format my specific types
         """

pandas/core/arrays/timedeltas.py

@@ -268,7 +268,7 @@ def _formatter(self, boxed=False):
         from pandas.io.formats.format import _get_format_timedelta64
         return _get_format_timedelta64(self, box=True)
 
-    def _format_native_types(self, na_rep=u'NaT', date_format=None):
+    def _format_native_types(self, na_rep='NaT', date_format=None):
         from pandas.io.formats.format import _get_format_timedelta64
 
         formatter = _get_format_timedelta64(self._data, na_rep)

pandas/core/indexes/period.py

@@ -395,7 +395,7 @@ def _maybe_convert_timedelta(self, other):
     # ------------------------------------------------------------------------
     # Rendering Methods
 
-    def _format_native_types(self, na_rep=u'NaT', quoting=None, **kwargs):
+    def _format_native_types(self, na_rep='NaT', quoting=None, **kwargs):
         # just dispatch, return ndarray
         return self._data._format_native_types(na_rep=na_rep,
                                                quoting=quoting,

pandas/core/indexes/timedeltas.py

@@ -224,7 +224,7 @@ def _formatter_func(self):
         from pandas.io.formats.format import _get_format_timedelta64
         return _get_format_timedelta64(self, box=True)
 
-    def _format_native_types(self, na_rep=u'NaT', date_format=None, **kwargs):
+    def _format_native_types(self, na_rep='NaT', date_format=None, **kwargs):
         from pandas.io.formats.format import Timedelta64Formatter
         return Timedelta64Formatter(values=self,
                                     nat_rep=na_rep,