Avoid Index DeprecationWarning in Series getitem (#31361)

* Avoid Index DeprecationWarning in Series getitem

xref #30867

Author: TomAugspurger

pandas/core/indexes/base.py

@@ -5832,6 +5832,8 @@ def deprecate_ndim_indexing(result):
         # GH#27125 indexer like idx[:, None] expands dim, but we
         #  cannot do that and keep an index, so return ndarray
         # Deprecation GH#30588
+        # Note: update SingleBlockManager.get_slice when the DeprecationWarning
+        # is elevated to a FutureWarning
         warnings.warn(
             "Support for multi-dimensional indexing (e.g. `index[:, None]`) "
             "on an Index is deprecated and will be removed in a future "

pandas/core/internals/managers.py

@@ -1505,7 +1505,7 @@ def get_slice(self, slobj, axis=0):
         if axis >= self.ndim:
             raise IndexError("Requested axis not found in manager")
 
-        return type(self)(self._block._slice(slobj), self.index[slobj], fastpath=True)
+        return type(self)(self._block._slice(slobj), self.index[slobj], fastpath=True,)
 
     @property
     def index(self):

pandas/core/series.py

@@ -940,7 +940,13 @@ def _get_with(self, key):
     def _get_values_tuple(self, key):
         # mpl hackaround
         if com.any_none(*key):
-            return self._get_values(key)
+            # suppress warning from slicing the index with a 2d indexer.
+            # eventually we'll want Series itself to warn.
+            with warnings.catch_warnings():
+                warnings.filterwarnings(
+                    "ignore", "Support for multi-dim", DeprecationWarning
+                )
+                return self._get_values(key)
 
         if not isinstance(self.index, MultiIndex):
             raise ValueError("Can only tuple-index with a MultiIndex")

pandas/tests/series/indexing/test_indexing.py

@@ -925,3 +925,13 @@ def test_uint_drop(any_int_dtype):
     series.loc[0] = 4
     expected = pd.Series([4, 2, 3], dtype=any_int_dtype)
     tm.assert_series_equal(series, expected)
+
+
+def test_getitem_2d_no_warning():
+    # https://github.com/pandas-dev/pandas/issues/30867
+    # Don't want to support this long-term, but
+    # for now ensure that the warning from Index
+    # doesn't comes through via Series.__getitem__.
+    series = pd.Series([1, 2, 3], index=[1, 2, 3])
+    with tm.assert_produces_warning(None):
+        series[:, None]

pandas/tests/series/test_timeseries.py

@@ -137,7 +137,12 @@ def test_first_last_valid(self, datetime_series):
         assert ts.last_valid_index().freq == ts.index.freq
 
     def test_mpl_compat_hack(self, datetime_series):
-        with tm.assert_produces_warning(DeprecationWarning, check_stacklevel=False):
+
+        # This is currently failing because the test was relying on
+        # the DeprecationWarning coming through Index.__getitem__.
+        # We want to implement a warning specifically for Series.__getitem__
+        # at which point this will become a Deprecation/FutureWarning
+        with tm.assert_produces_warning(None):
             # GH#30588 multi-dimensional indexing deprecated
             result = datetime_series[:, np.newaxis]
         expected = datetime_series.values[:, np.newaxis]