From 5a82ab1cf5c8dd19bd2092787dd8e593cc250f31 Mon Sep 17 00:00:00 2001
From: richard <rhshadrach@gmail.com>
Date: Wed, 16 Nov 2022 23:09:29 -0500
Subject: [PATCH 1/2] CLN: Handle no message for NotImplementedError in
 _cython_transform

---
 pandas/core/groupby/generic.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index 4ac701952e258..f73f5b2de5033 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -1362,8 +1362,9 @@ def arr_func(bvalues: ArrayLike) -> ArrayLike:
                 arr_func, ignore_failures=numeric_only is lib.no_default
             )
         except NotImplementedError as err:
-            # For NotImplementedError, args[0] is the error message
-            raise TypeError(err.args[0]) from err
+            # For NotImplementedError, args[0] is the error message when available
+            msg = err.args[0] if len(err.args) > 0 else ""
+            raise TypeError(msg) from err
         res_mgr.set_axis(1, mgr.axes[1])
 
         if len(res_mgr) < orig_mgr_len:

From 6e8cb2aafb3c1610f0803f9d45dc8bd9e725a506 Mon Sep 17 00:00:00 2001
From: Richard Shadrach <rhshadrach@gmail.com>
Date: Thu, 17 Nov 2022 17:09:05 -0500
Subject: [PATCH 2/2] Raise NotImplementedError

---
 pandas/core/groupby/generic.py        | 11 +++--------
 pandas/tests/groupby/test_function.py | 15 ++++++++++++---
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index f73f5b2de5033..32802f6429c4c 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -1357,14 +1357,9 @@ def arr_func(bvalues: ArrayLike) -> ArrayLike:
 
         # We could use `mgr.apply` here and not have to set_axis, but
         #  we would have to do shape gymnastics for ArrayManager compat
-        try:
-            res_mgr = mgr.grouped_reduce(
-                arr_func, ignore_failures=numeric_only is lib.no_default
-            )
-        except NotImplementedError as err:
-            # For NotImplementedError, args[0] is the error message when available
-            msg = err.args[0] if len(err.args) > 0 else ""
-            raise TypeError(msg) from err
+        res_mgr = mgr.grouped_reduce(
+            arr_func, ignore_failures=numeric_only is lib.no_default
+        )
         res_mgr.set_axis(1, mgr.axes[1])
 
         if len(res_mgr) < orig_mgr_len:
diff --git a/pandas/tests/groupby/test_function.py b/pandas/tests/groupby/test_function.py
index b848ff81f35ee..b66422836bbbf 100644
--- a/pandas/tests/groupby/test_function.py
+++ b/pandas/tests/groupby/test_function.py
@@ -250,6 +250,10 @@ def test_cummin_cummax(self, df, method):
     def _check(self, df, method, expected_columns, expected_columns_numeric):
         gb = df.groupby("group")
 
+        # object dtypes for transformations are not implemented in Cython and
+        # have no Python fallback
+        exception = NotImplementedError if method.startswith("cum") else TypeError
+
         if method in ("min", "max", "cummin", "cummax"):
             # The methods default to numeric_only=False and raise TypeError
             msg = "|".join(
@@ -258,7 +262,7 @@ def _check(self, df, method, expected_columns, expected_columns_numeric):
                     "function is not implemented for this dtype",
                 ]
             )
-            with pytest.raises(TypeError, match=msg):
+            with pytest.raises(exception, match=msg):
                 getattr(gb, method)()
         else:
             result = getattr(gb, method)()
@@ -274,7 +278,7 @@ def _check(self, df, method, expected_columns, expected_columns_numeric):
                     "function is not implemented for this dtype",
                 ]
             )
-            with pytest.raises(TypeError, match=msg):
+            with pytest.raises(exception, match=msg):
                 getattr(gb, method)(numeric_only=False)
         else:
             result = getattr(gb, method)(numeric_only=False)
@@ -1411,6 +1415,11 @@ def test_deprecate_numeric_only(
     elif has_arg or kernel in ("idxmax", "idxmin"):
         assert numeric_only is not True
         # kernels that are successful on any dtype were above; this will fail
+
+        # object dtypes for transformations are not implemented in Cython and
+        # have no Python fallback
+        exception = NotImplementedError if kernel.startswith("cum") else TypeError
+
         msg = "|".join(
             [
                 "not allowed for this dtype",
@@ -1422,7 +1431,7 @@ def test_deprecate_numeric_only(
                 "function is not implemented for this dtype",
             ]
         )
-        with pytest.raises(TypeError, match=msg):
+        with pytest.raises(exception, match=msg):
             method(*args, **kwargs)
     elif not has_arg and numeric_only is not lib.no_default:
         with pytest.raises(