Method column_setitem

pandas/core/internals/managers.py:1512–1542

Set values ("setitem") into a single column (not setting the full column). This is a method on the BlockManager level, to avoid creating an intermediate Series at the DataFrame level (`s = df[loc]; s[idx] = value`)

(
        self, loc: int, idx: int | slice | np.ndarray, value, inplace_only: bool = False
    )

        return

    def column_setitem(
        self, loc: int, idx: int | slice | np.ndarray, value, inplace_only: bool = False
    ) -> None:
        """
        Set values ("setitem") into a single column (not setting the full column).

        This is a method on the BlockManager level, to avoid creating an
        intermediate Series at the DataFrame level (`s = df[loc]; s[idx] = value`)
        """
        if not self._has_no_reference(loc):
            blkno = self.blknos[loc]
            # Split blocks to only copy the column we want to modify
            blk_loc = self.blklocs[loc]
            # Copy our values
            values = self.blocks[blkno].values
            if values.ndim == 1:
                values = values.copy()
            else:
                # Use [blk_loc] as indexer to keep ndim=2, this already results in a
                # copy
                values = values[[blk_loc]]
            self._iset_split_block(blkno, [blk_loc], values)

        # this manager is only created temporarily to mutate the values in place
        # so don't track references, otherwise the `setitem` would perform CoW again
        col_mgr = self.iget(loc, track_ref=False)
        if inplace_only:
            col_mgr.setitem_inplace(idx, value)
        else:
            new_mgr = col_mgr.setitem((idx,), value)
            self.iset(loc, new_mgr._block.values, inplace=True)

    def insert(self, loc: int, item: Hashable, value: ArrayLike, refs=None) -> None:
        """