CLN: move __finalize__ call into splitter (groupbt pandas-devGH-45363 follow-up)

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.

pandas/core/groupby/ops.py

@@ -705,17 +705,14 @@ def get_iterator(
         """
         splitter = self._get_splitter(data, axis=axis)
         keys = self.group_keys_seq
-        for key, group in zip(keys, splitter):
-            yield key, group.__finalize__(data, method="groupby")
+        yield from zip(keys, splitter)
 
     @final
     def _get_splitter(self, data: NDFrame, axis: int = 0) -> DataSplitter:
         """
         Returns
         -------
         Generator yielding subsetted objects
-
-        __finalize__ has not been called for the subsetted objects returned.
         """
         ids, _, ngroups = self.group_info
         return get_splitter(data, ids, ngroups, axis=axis)
@@ -753,7 +750,6 @@ def apply(
         zipped = zip(group_keys, splitter)
 
         for key, group in zipped:
-            group = group.__finalize__(data, method="groupby")
             object.__setattr__(group, "name", key)
 
             # group might be modified
@@ -1001,7 +997,6 @@ def _aggregate_series_pure_python(
         splitter = get_splitter(obj, ids, ngroups, axis=0)
 
         for i, group in enumerate(splitter):
-            group = group.__finalize__(obj, method="groupby")
             res = func(group)
             res = libreduction.extract_result(res)
 
@@ -1244,8 +1239,9 @@ class SeriesSplitter(DataSplitter):
     def _chop(self, sdata: Series, slice_obj: slice) -> Series:
         # fastpath equivalent to `sdata.iloc[slice_obj]`
         mgr = sdata._mgr.get_slice(slice_obj)
-        # __finalize__ not called here, must be applied by caller if applicable
-        return sdata._constructor(mgr, name=sdata.name, fastpath=True)
+        return sdata._constructor(mgr, name=sdata.name, fastpath=True).__finalize__(
+            sdata, method="groupby"
+        )
 
 
 class FrameSplitter(DataSplitter):
@@ -1256,8 +1252,7 @@ def _chop(self, sdata: DataFrame, slice_obj: slice) -> DataFrame:
         # else:
         #     return sdata.iloc[:, slice_obj]
         mgr = sdata._mgr.get_slice(slice_obj, axis=1 - self.axis)
-        # __finalize__ not called here, must be applied by caller if applicable
-        return sdata._constructor(mgr)
+        return sdata._constructor(mgr).__finalize__(sdata, method="groupby")
 
 
 def get_splitter(