Combinations in python using a generator

comb.py

from math import factorial as fact

def comb(seq, r):
	n = len(seq)
	total = fact(n) / (fact(r) * fact(n-r))
	pos = range(r)
	#c= []
	i = 0
	while i < total:		
		#c.append(map(lambda x: seq[x], pos))
		yield map(lambda x: seq[x], pos)
		k = r - 1		
		if pos[k] + 1 < n:			
			pos[k] = pos[k] + 1			
		else:			
			l = k - 1
			while l >= 0:
				if pos[l] + 1 < n - r + (l + 1):
					pos[l] = pos[l] + 1
					m = l + 1
					while m <= k:
						pos[m] = pos[m-1] + 1
						m = m + 1
					break	
				l = l - 1
		i = i + 1
	#return c

if __name__ == '__main__':	
    
	import pprint as pp
	a = comb('abcdef', 2)
	pp.pprint(list(a))
	print 'Total: ', len(list(a))