CLN: move __finalize__ call into splitter (groupbt GH-45363 follow-up) (#45415)

Author: jorisvandenbossche

pandas/core/generic.py

@@ -285,22 +285,6 @@ def _init_mgr(
                 mgr = mgr.astype(dtype=dtype)
         return mgr
 
-    @classmethod
-    def _from_mgr(cls, mgr: Manager):
-        """
-        Fastpath to create a new DataFrame/Series from just a BlockManager/ArrayManager.
-
-        Notes
-        -----
-        Skips setting `_flags` attribute; caller is responsible for doing so.
-        """
-        obj = cls.__new__(cls)
-        object.__setattr__(obj, "_is_copy", None)
-        object.__setattr__(obj, "_mgr", mgr)
-        object.__setattr__(obj, "_item_cache", {})
-        object.__setattr__(obj, "_attrs", {})
-        return obj
-
     def _as_manager(self: NDFrameT, typ: str, copy: bool_t = True) -> NDFrameT:
         """
         Private helper function to create a DataFrame with specific manager.