def get_column_letter(column_index):
    """
    Returns the spreadsheet column letter that corresponds to a given index (e.g.: 0 -> 'A', 3 -> 'D')

    Args:
        column_index (int):

    Returns:
        str: The column index expressed as a letter
    """
    if column_index > 25:
        raise ValueError("Cannot generate a column letter past 'Z'")
    uppercase_a_ord = ord("A")
    return chr(column_index + uppercase_a_ord)