Convert an excel or spreadsheet column letter to its number in Pythonic fashion

Question

Is there a more pythonic way of converting excel-style columns to numbers (starting with 1)?

Working code up to two letters:

Answer 1

I made this one-liner:

colNameToNum = lambda cn: sum([((ord(cn[-1-pos]) - 64) * 26 ** pos) for pos in range(len(cn))])

It works by iterating through the letters in reverse order and multiplying by 1, 26, 26 * 26 etc, then summing the list. This method would be compatible with longer strings of letters, too.

I call it with:

print(colNameToNum("AA")) # 27

or

print(colNameToNum("XFD")) # the highest column allowed, I believe. Result = 16384