Convert spreadsheet column letters (A,B, …, Z, AA, AB, …) to index numbers, and vice versa

spreadsheet_columns.py

def col_index(col):
	"""Take a spreadsheet-style column specifier, e.g. A, M, ZZ,
	and convert it to a one-based column index: A=1, Z=26, AA=27, etc.
	"""
	if not col or set(col) - set("ABCDEFGHIJKLMNOPQRSTUVWXYZ"):
		raise Exception("Bad column specifier: '" + col + "'")
	return reduce(lambda x,c: 26 * x + ord(c) - 64, col, 0)

def col_letters(index):
	"""Take a one-based column index and convert it to a
	spreadsheet-style column specifier: 1=A, 26=Z, 27=AA, etc.
	"""
	col_spec = ""
	while index:
		index, r = divmod(index - 1, 26)
		col_spec = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"[r] + col_spec
	return col_spec