DEPR: passing pandas type to Index.view (#58047)

Author: jbrockmendel

doc/source/whatsnew/v3.0.0.rst

@@ -206,6 +206,7 @@ Removal of prior version deprecations/changes
 - :meth:`SeriesGroupBy.agg` no longer pins the name of the group to the input passed to the provided ``func`` (:issue:`51703`)
 - All arguments except ``name`` in :meth:`Index.rename` are now keyword only (:issue:`56493`)
 - All arguments except the first ``path``-like argument in IO writers are now keyword only (:issue:`54229`)
+- Disallow passing a pandas type to :meth:`Index.view` (:issue:`55709`)
 - Removed "freq" keyword from :class:`PeriodArray` constructor, use "dtype" instead (:issue:`52462`)
 - Removed deprecated "method" and "limit" keywords from :meth:`Series.replace` and :meth:`DataFrame.replace` (:issue:`53492`)
 - Removed the "closed" and "normalize" keywords in :meth:`DatetimeIndex.__new__` (:issue:`52628`)

pandas/core/indexes/base.py

@@ -1013,7 +1013,7 @@ def ravel(self, order: str_t = "C") -> Self:
     def view(self, cls=None):
         # we need to see if we are subclassing an
         # index type here
-        if cls is not None and not hasattr(cls, "_typ"):
+        if cls is not None:
             dtype = cls
             if isinstance(cls, str):
                 dtype = pandas_dtype(cls)
@@ -1030,16 +1030,6 @@ def view(self, cls=None):
 
             result = self._data.view(cls)
         else:
-            if cls is not None:
-                warnings.warn(
-                    # GH#55709
-                    f"Passing a type in {type(self).__name__}.view is deprecated "
-                    "and will raise in a future version. "
-                    "Call view without any argument to retain the old behavior.",
-                    FutureWarning,
-                    stacklevel=find_stack_level(),
-                )
-
             result = self._view()
         if isinstance(result, Index):
             result._id = self._id

pandas/tests/indexes/numeric/test_numeric.py

@@ -312,8 +312,8 @@ def test_cant_or_shouldnt_cast(self, dtype):
 
     def test_view_index(self, simple_index):
         index = simple_index
-        msg = "Passing a type in .*Index.view is deprecated"
-        with tm.assert_produces_warning(FutureWarning, match=msg):
+        msg = "Cannot change data-type for object array"
+        with pytest.raises(TypeError, match=msg):
             index.view(Index)
 
     def test_prevent_casting(self, simple_index):

pandas/tests/indexes/ranges/test_range.py

@@ -200,11 +200,6 @@ def test_view(self):
         i_view = i.view("i8")
         tm.assert_numpy_array_equal(i.values, i_view)
 
-        msg = "Passing a type in RangeIndex.view is deprecated"
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            i_view = i.view(RangeIndex)
-        tm.assert_index_equal(i, i_view)
-
     def test_dtype(self, simple_index):
         index = simple_index
         assert index.dtype == np.int64
@@ -380,8 +375,8 @@ def test_cant_or_shouldnt_cast(self, start, stop, step):
 
     def test_view_index(self, simple_index):
         index = simple_index
-        msg = "Passing a type in RangeIndex.view is deprecated"
-        with tm.assert_produces_warning(FutureWarning, match=msg):
+        msg = "Cannot change data-type for object array"
+        with pytest.raises(TypeError, match=msg):
             index.view(Index)
 
     def test_prevent_casting(self, simple_index):

pandas/tests/indexes/test_datetimelike.py

@@ -85,15 +85,12 @@ def test_str(self, simple_index):
     def test_view(self, simple_index):
         idx = simple_index
 
-        idx_view = idx.view("i8")
         result = type(simple_index)(idx)
         tm.assert_index_equal(result, idx)
 
-        msg = "Passing a type in .*Index.view is deprecated"
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            idx_view = idx.view(type(simple_index))
-        result = type(simple_index)(idx)
-        tm.assert_index_equal(result, idx_view)
+        msg = "Cannot change data-type for object array"
+        with pytest.raises(TypeError, match=msg):
+            idx.view(type(simple_index))
 
     def test_map_callable(self, simple_index):
         index = simple_index

pandas/tests/indexes/test_old_base.py

@@ -891,10 +891,10 @@ def test_view(self, simple_index):
         idx_view = idx.view(dtype)
         tm.assert_index_equal(idx, index_cls(idx_view, name="Foo"), exact=True)
 
-        msg = "Passing a type in .*Index.view is deprecated"
-        with tm.assert_produces_warning(FutureWarning, match=msg):
-            idx_view = idx.view(index_cls)
-        tm.assert_index_equal(idx, index_cls(idx_view, name="Foo"), exact=True)
+        msg = "Cannot change data-type for object array"
+        with pytest.raises(TypeError, match=msg):
+            # GH#55709
+            idx.view(index_cls)
 
     def test_insert_non_na(self, simple_index):
         # GH#43921 inserting an element that we know we can hold should