Make _na_value a class attribute.

Author: goyodiaz

pandas/core/index.py

@@ -393,9 +393,8 @@ def values(self):
     def get_values(self):
         return self.values
 
-    def _na_value(self):
-        # The expected NA value to use with this index.
-        return np.nan
+    _na_value = np.nan
+    """The expected NA value to use with this index."""
 
     @property
     def is_monotonic(self):
@@ -2261,7 +2260,7 @@ def get_level_values(self, level):
         unique_vals = self.levels[num]  # .values
         labels = self.labels[num]
         values = Index(com.take_1d(unique_vals.values, labels,
-                                   fill_value=unique_vals._na_value()))
+                                   fill_value=unique_vals._na_value))
         values.name = self.names[num]
         return values
 

pandas/tseries/index.py

@@ -495,9 +495,8 @@ def _mpl_repr(self):
         # how to represent ourselves to matplotlib
         return tslib.ints_to_pydatetime(self.asi8, self.tz)
 
-    def _na_value(self):
-        # The expected NA value to use with this index.
-        return tslib.NaT
+    _na_value = tslib.NaT
+    """The expected NA value to use with this index."""
 
     def __unicode__(self):
         from pandas.core.format import _format_datetime64