Python xlsxwriter logic separation between row creation and insertion. `form_excel` function is independent of data inserted and header rows.

xlsxwriter_logic.py

from collections.abc import Iterable, Sequence
from typing import TypeVar, TypedDict

import xlsxwriter
from .items import Item

T = TypeVar("T")


class Data(TypedDict):
    a: int
    b: str

class ExcelRow(Sequence):
    def __init__(
        self, values: Iterable[T] | None = None, format: dict | None = None
    ) -> None:
        self.values = values or []
        self.format = format

    def __len__(self) -> int:
        return len(self.values)

    def __getitem__(self, index: int) -> T:
        return self.values[index]


class DataXLSXWriter:
    def __init__(
        self, items: Iterable[Item], dt_start: date, dt_end: date
    ) -> None:
        self.items = items
        self.dt_start = dt_start
        self.dt_end = dt_end

        self.output_dt_start = self.dt_start.strftime(DATE_FORMAT)
        self.output_dt_end = self.dt_end.strftime(DATE_FORMAT)
        self.output_today = date.today().strftime(DATE_FORMAT)

    def _get_data_rows(self) -> list[Data]:
        """Returns data."""
        return list[
            {"a": 10, "b": "hello world"},
            {"a": 1001, "b": "!"},
            {"a": 2, "b": "simple data"},
        ]

    def _get_header_rows(self) -> list[ExcelRow[Data]]:
        """Returns header rows that do not contain stats data."""
        date_format = {"num_format": "yyyy-mm-dd"}
        center_format = {"valign": "center"}
        bold_format = {"bold": True}

        header_rows: list[ExcelRow] = [
            ExcelRow(
                ["Date create", "Date start", "Date end"],
                center_format,
            ),
            ExcelRow(
                [
                    self.output_today,
                    self.output_dt_start,
                    self.output_dt_end,
                ],
                center_format | date_format,
            ),
            ExcelRow(
                ["Item", "Make"],  # rows can be of variable length
                bold_format | center_format,
            ),
            ExcelRow(),  # supports empty rows
        ]
        return header_rows

    def form_excel(self, filename: str) -> None:
        """Creates Excel file.

        Parameters
        ----------
        filename : str
            Resulting Excel file name.
        """
        with xlsxwriter.Workbook(filename, {"in_memory": True}) as workbook:
            worksheet = workbook.add_worksheet()

            for shared_index, row in enumerate(
                self._get_header_rows(), start=1
            ):
                worksheet.write_row(
                    f"A{shared_index}",
                    row,
                    workbook.add_format(row.format),
                )
            for index, item in enumerate(
                self._get_data_rows(), start=shared_index + 1
            ):
                worksheet.write_row(f"A{index}", item.values())

            worksheet.autofit()