Input

def read_identifiers(
    filename: str | Path,
) -> list[SecurityIdentifier]:
    """Read security identifiers from an Excel file.

    The input file must contain the columns ``Type`` and ``Value``.
    ``Type`` may be omitted or empty. In that case the identifier type
    is detected automatically for ISINs and tickers.
    """

    path = Path(filename)
    workbook = load_workbook(path, read_only=True, data_only=True)

    try:
        worksheet = workbook.active
        rows = worksheet.iter_rows(values_only=True)

        headers = next(rows, None)
        if headers is None:
            return []

        header_map = _get_header_map(headers)
        if "value" not in header_map:
            message = "Input file must contain a 'Value' column."
            raise ValueError(message)

        return [
            _create_identifier(row, header_map, row_number)
            for row_number, row in enumerate(rows, start=2)
        ]
    finally:
        workbook.close()