nextBigger by permutation

import itertools
def nextBigger(n):
    b=10*n
    digits = [int(d) for d in str(n)]
    perm=set(itertools.permutations(digits))
    lst=list(perm)
    for j in range (len(lst)):
        num = int("".join(map(str, lst[j])))
        if n<num and num<b:
            b=num

    if n<b and b<10*n:
        return (b)
    else:
        return (-1)