Remove redundant copying

pandas/core/generic.py

@@ -1219,7 +1219,7 @@ def _slice(self, slobj, axis=0, kind=None):
  def _set_item(self, key, value):
 
  # If children are views, reset to copies before setting.
- self._convert_views_to_copies()
+ self._execute_copy_on_write()
 
  self._data.set(key, value)
  self._clear_item_cache()
@@ -1233,23 +1233,13 @@ def _set_is_copy(self, ref=None, copy=True):
  else:
  self.is_copy = None
 
- def _convert_views_to_copies(self):
+ def _execute_copy_on_write(self):
 
  # Don't set on views. 
- if self._is_view and not self._is_column_view:
+ if (self._is_view and not self._is_column_view) or len(self._children) is not 0:
  self._data = self._data.copy()
-
-
- # Before setting values, make sure children converted to copies. 
- for child in self._children.valuerefs():
-
- # Make sure children of children converted. 
- child()._convert_views_to_copies()
-
- if child()._is_view and not child()._is_column_view:
- child()._data = child()._data.copy()
+ self._children = weakref.WeakValueDictionary()
 
- self._children = weakref.WeakValueDictionary()
 
  def _add_to_children(self, view_to_append):
  self._children[id(view_to_append)] = view_to_append

pandas/core/indexing.py

@@ -115,7 +115,7 @@ def _get_setitem_indexer(self, key):
 
  def __setitem__(self, key, value):
  # Make sure changes don't propagate to children
- self.obj._convert_views_to_copies()
+ self.obj._execute_copy_on_write()
 
  indexer = self._get_setitem_indexer(key)
  self._setitem_with_indexer(indexer, value)

pandas/tests/test_generic.py

@@ -1745,7 +1745,6 @@ def test_copy_on_write(self):
 
  for v in views.keys():
  tm.assert_frame_equal(views[v], copies[v])
- self.assertFalse(views[v]._is_view)
 
  # Test different forms of value setting 
  # all trigger conversions
@@ -1768,7 +1767,6 @@ def test_copy_on_write(self):
 
  for v in views.keys():
  tm.assert_frame_equal(views[v], copies[v])
- self.assertFalse(views[v]._is_view)
 
  ########
  # No Backward Propogation