TypeError: 'int' object is not iterable

def quick_sort(lst,l,r):
    if(l<r):
        i=l,j=r,x=lst[l]
        while(i<j):
            while(i<j and lst[j]>=x):
                j-=1
            if(i<j):
                lst[i]=lst[j]
                i+=1
            while(i<j and lst[j]<x):
                i+=1
            if(i<j):
                lst[j]=lst[i]
                j-=1
        lst[i]=x
        quick_sort(lst,l,i-1)
        quick_sort(lst,i+1,r)




if __name__ == '__main__':
    lst=[5,3,12,63,25,78,17,19,60]
    quick_sort(lst,0,len(lst)-1)
    for item in lst:
        print item

报错信息：
Traceback (most recent call last):
File "C:/Users/LYH/PycharmProjects/untitled7/sort.py", line 22, in
quick_sort(lst,0,len(lst)-1)
File "C:/Users/LYH/PycharmProjects/untitled7/sort.py", line 3, in quick_sort
i = l, j = r,x = lst[l]
TypeError: 'int' object is not iterable

请问我在哪里将int进行了迭代？

s[i]=x
s在哪里定义的？