Print Segment Code

def printvalidsegments(string,wset):
    # 'wset' gives the set of valid words
    # 'string' is the string to be segmented

    valid = 0   # index till which it has been validified
    last_letter_index = len(string)

    vseglist = [] #list storing all valid segments
    segflag = False #indicating whether any valid segment has been found
    while valid != last_letter_index :
        ran = xrange(last_letter_index,valid,-1)
        for i in ran:
            if string[valid:i].lower() in wset:

                segflag = True #valid segmnt has been found
                #print "debug:segment",string[valid:i],valid,i
                vseglist.append(string[valid:i]) #segmnt has been added to list
                valid = i
                break

            if i == (valid+1):
                for seg in vseglist: #backtracking: try removing one valid segment from wset and hence continue
                    #print "debug:first",seg
                    wset.remove(seg.lower())
                    if printvalidsegments(string,wset):
                        return True
                    wset.add(seg.lower())

                valid = last_letter_index
                return False
    print  " ".join(vseglist)
    return True

def main():
    string = "artisteer"
    wset = set(['art','i','steer','artist','a','sign','as'])
    if printvalidsegments(string,wset) == False:
        print "error"

    string = "asignas"
    if printvalidsegments(string,wset) == False: #prints error instead of valid segments "a sign as"
        print "error"


if __name__ == '__main__':
    main()