def DirectoryAttack(A,B=[]):
    if len(B)<1:
        B=A
    for i in xrange(0,len(A)):
        for j in xrange(0,len(B)):
            ijgcd = gcd(A[i],B[j])
            if (ijgcd>1) and (A[i]!=B[j]):
                print ("The common factor of {0} and {1} is {2}".format(A[i],B[j],ijgcd))

DirectoryAttack([1,2,3],[3,6,7])