Towers oh hanoi

def ToH(sourcen,destn,sparen,n,source=None,destination=None, spare=None,printer=None):
        if source == None:
                source = range(1,n+1)[::-1]
                destination = []
                spare = []
                printer = []
        if n==1:
                printer.append( "Move disk" + str(source[-1]) + " from " + str(sourcen) + " to " + str(destn))
                #print len(printer)

                destination.append(source.pop())
        else:
                printer += ToH(sourcen,sparen,destn,(n-1),source,spare,destination,printer)
                printer += ToH(sourcen,destn,sparen,1,source,destination,spare,printer)
                printer += ToH(sparen,destn,sourcen,(n-1),spare, destination, source,printer)
        if len(printer)>100:
                print "!!"
                print printer[99]
                print ""
                raise("Problem")
        return printer

print "starting..."
ToH("A","B","C",13)