Combinations of keywords in matrix

combinations.py

def combinations(keywords, opts):
   if len(keywords) == 0:
     return [[]]
   else:
     res = []
     for opt in opts[keywords[0]]:
       for combination in combinations(keywords[1:], opts):
         res.append([opt] + combination)
     return res
 
 keywords = ['a', 'b']
 opts = { 'a': ['a1', 'a2'], 'b': ['b1', 'b2']}
 for combination in combinations(keywords, opts):
   print combination