COMPAT: remove SettingWithCopy warning, and use copy-on-write, #10954

pandas/core/common.py

@@ -26,15 +26,12 @@
 class PandasError(Exception):
     pass
 
-
-class SettingWithCopyError(ValueError):
+class SettingImmutableError(ValueError):
     pass
 
-
-class SettingWithCopyWarning(Warning):
+class SettingWithCopyError(ValueError):
     pass
 
-
 class AmbiguousIndexError(PandasError, KeyError):
     pass
 

pandas/core/config_init.py

@@ -321,13 +321,12 @@ def use_inf_as_null_cb(key):
 # user warnings
 chained_assignment = """
 : string
-    Raise an exception, warn, or no action if trying to use chained assignment,
-    The default is warn
+  this option has been deprecated and has no effect
 """
 
-with cf.config_prefix('mode'):
-    cf.register_option('chained_assignment', 'warn', chained_assignment,
-                       validator=is_one_of_factory([None, 'warn', 'raise']))
+cf.register_option('mode.chained_assignment', 'warn', chained_assignment,
+                   validator=is_one_of_factory([None, 'warn', 'raise']))
+cf.deprecate_option('mode.chained_assignment', chained_assignment)
 
 
 # Set up the io.excel specific configuration.

pandas/core/frame.py

@@ -1825,7 +1825,7 @@ def _ixs(self, i, axis=0):
                     copy = isinstance(new_values,np.ndarray) and new_values.base is None
                     result = Series(new_values, index=self.columns,
                                     name=self.index[i], dtype=new_values.dtype)
-                result._set_is_copy(self, copy=copy)
+                result._set_parent(self, copy=copy)
                 return result
 
         # icol
@@ -1957,7 +1957,7 @@ def _getitem_multilevel(self, key):
                     if isinstance(result, Series):
                         result = self._constructor_sliced(result, index=self.index, name=key)
 
-            result._set_is_copy(self)
+            result._set_parent(self)
             return result
         else:
             return self._get_item_cache(key)
@@ -2229,7 +2229,7 @@ def __setitem__(self, key, value):
             self._set_item(key, value)
 
     def _setitem_slice(self, key, value):
-        self._check_setitem_copy()
+        self._check_copy_on_write()
         self.ix._setitem_with_indexer(key, value)
 
     def _setitem_array(self, key, value):
@@ -2240,7 +2240,7 @@ def _setitem_array(self, key, value):
                                  (len(key), len(self.index)))
             key = check_bool_indexer(self.index, key)
             indexer = key.nonzero()[0]
-            self._check_setitem_copy()
+            self._check_copy_on_write()
             self.ix._setitem_with_indexer(indexer, value)
         else:
             if isinstance(value, DataFrame):
@@ -2250,7 +2250,7 @@ def _setitem_array(self, key, value):
                     self[k1] = value[k2]
             else:
                 indexer = self.ix._convert_to_indexer(key, axis=1)
-                self._check_setitem_copy()
+                self._check_copy_on_write()
                 self.ix._setitem_with_indexer((slice(None), indexer), value)
 
     def _setitem_frame(self, key, value):
@@ -2260,7 +2260,7 @@ def _setitem_frame(self, key, value):
             raise TypeError('Must pass DataFrame with boolean values only')
 
         self._check_inplace_setting(value)
-        self._check_setitem_copy()
+        self._check_copy_on_write()
         self.where(-key, value, inplace=True)
 
     def _ensure_valid_index(self, value):
@@ -2293,14 +2293,20 @@ def _set_item(self, key, value):
         """
 
         self._ensure_valid_index(value)
-        value = self._sanitize_column(key, value)
-        NDFrame._set_item(self, key, value)
-
-        # check if we are modifying a copy
-        # try to set first as we want an invalid
-        # value exeption to occur first
-        if len(self):
-            self._check_setitem_copy()
+        svalue = self._sanitize_column(key, value)
+        try:
+            NDFrame._set_item(self, key, svalue)
+        except com.SettingWithCopyError:
+
+            # if we have a multi-index (which potentially has dropped levels)
+            # need to raise
+            for p in self._parent:
+                if isinstance(getattr(p(),'columns',None), MultiIndex):
+                    raise
+
+            # we have a chained assignment
+            # assign back to the original
+            self._parent[0]().loc[self.index,key] = value
 
     def insert(self, loc, column, value, allow_duplicates=False):
         """