def intersect(seq1, seq2): res = [] # start empty for x in seq1: # scan seq1 if x in seq2: # common item? res.append(x) # add to end return res s1 = "SPAM" s2 = "SCAM" print intersect(s1, s2) # strings s1 = [1,2,3,4,5] s2 = [3,4,5,6,7] print intersect(s1, s2) # list