Excelのカラムの表記をインデックスを元に求める(0->A, 25->Z, 26->AAなど。インデックスは0始まり(Excelでは1始まり))

excel.ps1

function ColumnKey($idx)
{
	$excel = New-Object -ComObject Excel.Application
	$excel.Visible = $true
	$book = $excel.Workbooks.Add()
	$sheet = $book.Sheets(1)
	$cell = $sheet.Cells(1, 1)
	$col = $idx + 1
	$cell.Formula = "=ADDRESS(1,$($col),4)"
	$text = $cell.Text
	$_ = $book.Close($false)
	$_ = $excel.Quit()
	$_ = [System.Runtime.Interopservices.Marshal]::ReleaseComObject($excel)
	Remove-Variable excel
	return $text.Substring(0, $text.Length - 1)
}

ColumnKey(0) | echo
ColumnKey(1) | echo
ColumnKey(25) | echo
ColumnKey(26) | echo
ColumnKey(27) | echo
ColumnKey(72) | echo

excel.py

import pytest
@pytest.mark.parametrize('num,col',
    [
        (0, 'A'),
        (26, 'AA'),
        (72, 'BU'),
        (701, 'ZZ'),
        (702, 'AAA'),
        (1377, 'AZZ'),
        (1378, 'BAA'),
        (2054, 'CAA'),
        (16383, 'XFD'),
    ])
def test_column_key(num, col):
    assert column_key(num) == col
def test_column_key_max():
    with pytest.raises(ValueError):
        column_key(16384)
def column_key(num):
    if num > 16383:
        raise ValueError("maximum index of row is 16383")
    digits = 'ABCDEFGHIJKLMNOPQRSTUVEXYZ'
    base = len(digits)
    converted = digits[num % base]
    num = num // base
    while num > 0:
        converted = digits[num % base - 1] + converted
        num = (num - 1) // base
    return converted