TOSQUASH: ENH: _dir_additions returns only the 100 first values of th…

…e index' first level

pandas/core/generic.py

@@ -197,8 +197,9 @@ def _dir_additions(self):
         """ add the string-like attributes from the info_axis.
         If info_axis is a MultiIndex, it's first level values are used.
         """
-        additions = set([c for c in self._info_axis.get_level_values(0)
-                         if isinstance(c, string_types) and isidentifier(c)])
+        additions = set(
+            [c for c in self._info_axis.unique(level=0)[:100]
+             if isinstance(c, string_types) and isidentifier(c)])
         return super(NDFrame, self)._dir_additions().union(additions)
 
     @property