Merge split adjustments with the dict containing overwrites.

        Parameters
        ----------
        pre : dict[str -> dict[int -> list]]
            The adjustments that occur before the split-adjusted-asof-date.
        post : dict[str -> dict[int -> list]]
            The adjustments that occur after the split-adjusted-asof-date.
        overwrites : dict[str -> dict[int -> list]]
            The overwrites across all time. Adjustments will be merged into
            this dictionary.
        requested_split_adjusted_columns : list of str
            List of names of split adjusted columns that are being requested.

def merge_split_adjustments_with_overwrites(
        self,
        pre,
        post,
        overwrites,
        requested_split_adjusted_columns
    ):
        """
        Merge split adjustments with the dict containing overwrites.

        Parameters
        ----------
        pre : dict[str -> dict[int -> list]]
            The adjustments that occur before the split-adjusted-asof-date.
        post : dict[str -> dict[int -> list]]
            The adjustments that occur after the split-adjusted-asof-date.
        overwrites : dict[str -> dict[int -> list]]
            The overwrites across all time. Adjustments will be merged into
            this dictionary.
        requested_split_adjusted_columns : list of str
            List of names of split adjusted columns that are being requested.
        """
        for column_name in requested_split_adjusted_columns:
            # We can do a merge here because the timestamps in 'pre' and
            # 'post' are guaranteed to not overlap.
            if pre:
                # Either empty or contains all columns.
                for ts in pre[column_name]:
                    add_new_adjustments(
                        overwrites,
                        pre[column_name][ts],
                        column_name,
                        ts
                    )
            if post:
                # Either empty or contains all columns.
                for ts in post[column_name]:
                    add_new_adjustments(
                        overwrites,
                        post[column_name][ts],
                        column_name,
                        ts
                    )