Nearest Smaller to Left

Problem Link: https://www.interviewbit.com/problems/nearest-smaller-element/

class Solution:
    # @param arr : list of integers
    # @return a list of integers
    def prevSmaller(self, nums):
        
        s=[]
        n=len(nums)
        ans=[]
        for i in range(n):
            if(len(s)==0):
                ans.append(-1)
            else:
                if(s[-1]<nums[i]):
                    ans.append(s[-1])
                else:
                    while(len(s)>0 and s[-1]>=nums[i]):
                        s.pop()
                    if(len(s)==0):
                        ans.append(-1)
                    else:
                        ans.append(s[-1])
            s.append(nums[i])
        return ans