Leetcode: Next Permutation @Python

class Solution:
    # @param num, a list of integer
    # @return a list of integer
    def nextPermutation(self, num):
        k=len(num)
        if k==1:
            return num
        left=-1
        for i in range(k-2,-1,-1):
            if num[i]<num[i+1]:
                left=i
                break
        for i in range(k-1,-1,-1):
            if num[i]>num[left]:
                right=i
                break
        if left>=0:
            num[left],num[right]=num[right],num[left]
            l=left+1
        else:
            l=0
        while l<k-1:
            num[l],num[k-1]=num[k-1],num[l]
            l+=1
            k-=1
        return num