pretty print

def pretty_print(assignment):
    for i in range(9):
        output = ''
        for j in range(9):
            values = assignment[str(i) + "-" + str(j)]
            if len(values) == 1:
                output += " " + values[0] + " "
            else:
                output += "   "

            if j == 2 or j == 5:
                output += "|"
        print output
        if i == 2 or i == 5:
            print '---------+---------+---------'
    print " "
    print " "