ENH: revert Index mutability change. improve performance of dropna by using take. related to #2162

Author: wesm

pandas/core/frame.py

@@ -2709,9 +2709,7 @@ def dropna(self, axis=0, how='any', thresh=None, subset=None):
             else:
                 raise ValueError('must specify how or thresh')
 
-        labels = self._get_axis(axis)
-        new_labels = labels[mask]
-        return self.reindex(**{axis_name: new_labels})
+        return self.take(mask.nonzero()[0], axis=axis)
 
     def drop_duplicates(self, cols=None, take_last=False, inplace=False):
         """

pandas/core/index.py

@@ -305,11 +305,8 @@ def __contains__(self, key):
     def __hash__(self):
         return hash(self.view(np.ndarray))
 
-    def __getattribute__(self,name):
-        if name=="__setitem__": # emulate an Immutable ndarray
-            raise AttributeError(str(self.__class__) + ' object is immutable')
-        else:
-            return object.__getattribute__(self,name)
+    def __setitem__(self, key, value):
+        raise Exception(str(self.__class__) + ' object is immutable')
 
     def __getitem__(self, key):
         """Override numpy.ndarray's __getitem__ method to work as desired"""

pandas/tests/test_format.py

@@ -765,7 +765,7 @@ def test_to_html_with_classes(self):
             <table border="1" class="dataframe sortable draggable">
               <tbody>
                 <tr>
-                  <td>Index((), dtype=object)</td>
+                  <td>Index([], dtype=object)</td>
                   <td>Empty DataFrame</td>
                 </tr>
               </tbody>

pandas/tests/test_index.py

@@ -57,7 +57,7 @@ def test_sort(self):
         self.assertRaises(Exception, self.strIndex.sort)
 
     def test_mutability(self):
-        self.assertFalse(hasattr(self.strIndex,"__setitem__"))
+        self.assertRaises(Exception, self.strIndex.__setitem__, 0, 'foo')
 
     def test_constructor(self):
         # regular instance creation