DEPR: pandas.core for groupby

Author: rhshadrach

pandas/core/common.py

@@ -650,3 +650,15 @@ def fill_missing_names(names: Sequence[Hashable | None]) -> list[Hashable]:
         list of column names with the None values replaced.
     """
     return [f"level_{i}" if name is None else name for i, name in enumerate(names)]
+
+
+def _depr_core() -> None:
+    warnings.warn(
+        "pandas.core is deprecated and has been renamed to "
+        "pandas._core. Accessing `_core` directly is discouraged as "
+        "members can change without warning.  You should use a public module "
+        "instead that exports the attribute in question. If you still would "
+        "like to access an attribute from it, please use pandas._core.",
+        DeprecationWarning,
+        stacklevel=3,
+    )

pandas/meson.build

@@ -26,6 +26,7 @@ subdir('_libs')
 
 subdirs_list = [
     '_config',
+    '_core',
     '_testing',
     'api',
     'arrays',

pandas/tests/api/test_api.py

@@ -381,3 +381,23 @@ def test_pandas_array_alias():
         res = pd.arrays.PandasArray
 
     assert res is pd.arrays.NumpyExtensionArray
+
+
+@pytest.mark.parametrize("submodule_name", ["groupby"])
+def test_depr_pandas_core_submodule(submodule_name):
+    # GH#27522
+
+    submodule = getattr(pd._core, submodule_name)
+    warning_msg = "pandas.core is deprecated"
+    for submodule_member_name in dir(submodule):
+        if submodule_member_name.startswith("__") and submodule_member_name.endswith(
+            "__"
+        ):
+            continue
+        submodule_member = getattr(submodule, submodule_member_name)
+        with tm.assert_produces_warning(DeprecationWarning, match=warning_msg):
+            core_submodule = __import__(
+                f"pandas.core.{submodule_name}", fromlist=[submodule_member_name]
+            )
+        with tm.assert_produces_warning(DeprecationWarning, match=warning_msg):
+            assert submodule_member is getattr(core_submodule, submodule_member_name)

scripts/validate_unwanted_patterns.py

@@ -55,6 +55,8 @@
     "_iLocIndexer",
     # TODO(3.0): GH#55043 - remove upon removal of ArrayManager
     "_get_option",
+    # GH#27522
+    "_depr_core",
 }