DEPR: removed deprecated argument obj from GroupBy get_group

doc/source/whatsnew/v3.0.0.rst

@@ -96,6 +96,13 @@ Deprecations
 - Deprecated :meth:`Timestamp.utcnow`, use ``Timestamp.now("UTC")`` instead (:issue:`56680`)
 -
 
+.. ---------------------------------------------------------------------------
+.. _whatsnew_300.prior_deprecations:
+
+Removal of prior version deprecations/changes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+- Removed deprecated argument ``obj`` in :meth:`GroupBy.get_group` (:issue:`53545`)
+
 .. ---------------------------------------------------------------------------
 .. _whatsnew_300.performance:
 

pandas/core/groupby/groupby.py

@@ -1062,15 +1062,14 @@ def get_group(self, name, obj=None) -> DataFrame | Series:
             it is None, the object groupby was called on will
             be used.
 
-            .. deprecated:: 2.1.0
-                The obj is deprecated and will be removed in a future version.
-                Do ``df.iloc[gb.indices.get(name)]``
-                instead of ``gb.get_group(name, obj=df)``.
-
         Returns
         -------
         same type as obj
 
+        Raises
+        ------
+        ValueError : The passed argument obj is not None.
+
         Examples
         --------
 
@@ -1146,14 +1145,7 @@ def get_group(self, name, obj=None) -> DataFrame | Series:
             indexer = inds if self.axis == 0 else (slice(None), inds)
             return self._selected_obj.iloc[indexer]
         else:
-            warnings.warn(
-                "obj is deprecated and will be removed in a future version. "
-                "Do ``df.iloc[gb.indices.get(name)]`` "
-                "instead of ``gb.get_group(name, obj=df)``.",
-                FutureWarning,
-                stacklevel=find_stack_level(),
-            )
-            return obj._take_with_is_copy(inds, axis=self.axis)
+            raise ValueError("cannot pass argument obj to get_group")
 
     @final
     def __iter__(self) -> Iterator[tuple[Hashable, NDFrameT]]:

pandas/tests/groupby/test_groupby.py

@@ -527,13 +527,11 @@ def test_as_index_select_column():
 
 
 def test_obj_arg_get_group_deprecated():
-    depr_msg = "obj is deprecated"
+    msg = "cannot pass argument obj to get_group"
 
     df = DataFrame({"a": [1, 1, 2], "b": [3, 4, 5]})
-    expected = df.iloc[df.groupby("b").indices.get(4)]
-    with tm.assert_produces_warning(FutureWarning, match=depr_msg):
-        result = df.groupby("b").get_group(4, obj=df)
-        tm.assert_frame_equal(result, expected)
+    with pytest.raises(ValueError, match=msg):
+        df.groupby("b").get_group(4, obj=df)
 
 
 def test_groupby_as_index_select_column_sum_empty_df():