Python-如何优化代码以减少执行时间？

Question

该脚本以指数形式增加数字时显示（0,1,2,3,4,5,6,7,8,9）中出现的最后一个数字。

我认为我的问题集中在循环上。

def EjA(n):
    #List of numbers to control
    l1=[0,1,2,3,4,5,6,7,8,9]
    #Convert l2 to str
    l2=''.join(map(str,l1))
    l3=[]
    #List of deleted elements
    l_item_deleted=[]
    cont=1
    #Conditional to check n is between 1 and 10000
    if n<=1 or n>= 10000:
        return None
    else:
        #To delete data until have just the last number
        while len(l2)>1:
            #Add to l3 n**cont to collect all the number in l3 list
            l3.append(n**cont)
            #Convert l3 to str
            l4=''.join(map(str,l3))
            l_item_deleted_aux=''.join(map(str,l_item_deleted))
            #Delete the element deleted before
            l4=l4.replace(l_item_deleted_aux,'')
            cont+=1
            for i in l4:
                if (i in l2) and len(l2)>1:
                    #Delete from l2 all the numbers which appear in l4
                    l2=l2.replace(i,'')
                    #Collect the element deleted in a list
                    l_item_deleted.append(i)
                elif (i not in l2) and len(l2)>1:
                    l_item_deleted.append(i)
        return int(l2)
EjA(2)

目前，我的执行时间过长，无法完成所有测试随机案例。

目标是改进代码以减少执行时间。

一些建议？