CLN/DEPR: remove setter for MultiIndex levels/labels properties

doc/source/whatsnew/v0.22.0.txt

@@ -62,7 +62,7 @@ Removal of prior version deprecations/changes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 - Warnings against the obsolete usage ``Categorical(codes, categories)``, which were emitted for instance when the first two arguments to ``Categorical()`` had different dtypes, and recommended the use of ``Categorical.from_codes``, have now been removed (:issue:`8074`)
--
+- The ``levels`` and ``labels`` attributes of a ``MultiIndex`` can no longer be set directly (:issue:`4039`).
 -
 
 .. _whatsnew_0220.performance:

pandas/core/indexes/multi.py

@@ -2,7 +2,6 @@
 # pylint: disable=E1101,E1103,W0232
 import datetime
 import warnings
-from functools import partial
 from sys import getsizeof
 
 import numpy as np
@@ -28,8 +27,7 @@
                                 is_true_slices)
 
 import pandas.core.base as base
-from pandas.util._decorators import (Appender, cache_readonly,
-                                     deprecate, deprecate_kwarg)
+from pandas.util._decorators import Appender, cache_readonly, deprecate_kwarg
 import pandas.core.common as com
 import pandas.core.missing as missing
 import pandas.core.algorithms as algos
@@ -177,7 +175,8 @@ def _verify_integrity(self, labels=None, levels=None):
                                  " inconsistent state" % (i, label.max(),
                                                           len(level)))
 
-    def _get_levels(self):
+    @property
+    def levels(self):
         return self._levels
 
     def _set_levels(self, levels, level=None, copy=False, validate=True,
@@ -279,14 +278,8 @@ def set_levels(self, levels, level=None, inplace=False,
         if not inplace:
             return idx
 
-    # remove me in 0.14 and change to read only property
-    __set_levels = deprecate("setting `levels` directly",
-                             partial(set_levels, inplace=True,
-                                     verify_integrity=True),
-                             alt_name="set_levels")
-    levels = property(fget=_get_levels, fset=__set_levels)
-
-    def _get_labels(self):
+    @property
+    def labels(self):
         return self._labels
 
     def _set_labels(self, labels, level=None, copy=False, validate=True,
@@ -379,13 +372,6 @@ def set_labels(self, labels, level=None, inplace=False,
         if not inplace:
             return idx
 
-    # remove me in 0.14 and change to readonly property
-    __set_labels = deprecate("setting labels directly",
-                             partial(set_labels, inplace=True,
-                                     verify_integrity=True),
-                             alt_name="set_labels")
-    labels = property(fget=_get_labels, fset=__set_labels)
-
     def copy(self, names=None, dtype=None, levels=None, labels=None,
              deep=False, _set_identity=False, **kwargs):
         """

pandas/tests/indexes/test_multi.py

@@ -158,6 +158,24 @@ def test_set_name_methods(self):
         assert res is None
         assert ind.names == new_names2
 
+    def test_set_levels_labels_directly(self):
+        # setting levels/labels directly raises AttributeError
+
+        levels = self.index.levels
+        new_levels = [[lev + 'a' for lev in level] for level in levels]
+
+        labels = self.index.labels
+        major_labels, minor_labels = labels
+        major_labels = [(x + 1) % 3 for x in major_labels]
+        minor_labels = [(x + 1) % 1 for x in minor_labels]
+        new_labels = [major_labels, minor_labels]
+
+        with pytest.raises(AttributeError):
+            self.index.levels = new_levels
+
+        with pytest.raises(AttributeError):
+            self.index.labels = new_labels
+
     def test_set_levels(self):
         # side note - you probably wouldn't want to use levels and labels
         # directly like this - but it is possible.
@@ -578,16 +596,6 @@ def test_constructor_mismatched_label_levels(self):
         with tm.assert_raises_regex(ValueError, label_error):
             self.index.copy().set_labels([[0, 0, 0, 0], [0, 0]])
 
-        # deprecated properties
-        with warnings.catch_warnings():
-            warnings.simplefilter('ignore')
-
-            with tm.assert_raises_regex(ValueError, length_error):
-                self.index.copy().levels = [['a'], ['b']]
-
-            with tm.assert_raises_regex(ValueError, label_error):
-                self.index.copy().labels = [[0, 0, 0, 0], [0, 0]]
-
     def assert_multiindex_copied(self, copy, original):
         # Levels should be (at least, shallow copied)
         tm.assert_copy(copy.levels, original.levels)