CLN: avoid catching Exception in _choose_path (#28205)

Author: jbrockmendel

pandas/core/groupby/generic.py

@@ -649,20 +649,21 @@ def _choose_path(self, fast_path, slow_path, group):
         # if we make it here, test if we can use the fast path
         try:
             res_fast = fast_path(group)
-
-            # verify fast path does not change columns (and names), otherwise
-            # its results cannot be joined with those of the slow path
-            if res_fast.columns != group.columns:
-                return path, res
-            # verify numerical equality with the slow path
-            if res.shape == res_fast.shape:
-                res_r = res.values.ravel()
-                res_fast_r = res_fast.values.ravel()
-                mask = notna(res_r)
-                if (res_r[mask] == res_fast_r[mask]).all():
-                    path = fast_path
         except Exception:
-            pass
+            # Hard to know ex-ante what exceptions `fast_path` might raise
+            return path, res
+
+        # verify fast path does not change columns (and names), otherwise
+        # its results cannot be joined with those of the slow path
+        if not isinstance(res_fast, DataFrame):
+            return path, res
+
+        if not res_fast.columns.equals(group.columns):
+            return path, res
+
+        if res_fast.equals(res):
+            path = fast_path
+
         return path, res
 
     def _transform_item_by_item(self, obj, wrapper):