我下面的python合并排序代码有什么问题?

合并排序

这是显示错误,我无法理解,请帮助合并排序,这是显示出索引,但我无法理解,如何请任何人更新,请帮助我?

def mergesort(a,low,high):
    if(low<high):
        mid=(high+low)//2
        mergesort(a,low,mid)
        mergesort(a,mid+1,high)
        merge(a,low,mid,high)
def merge(a,low,mid,high):
    i=low
    j=mid+1
    while(i<=mid and j<=high):
        if(a[i]<=a[j]):
            print(a[i])
            c.append(a[i])
            i+=1
        else:
            c.append(a[j])
            j+=1
a=[4,2,7,0,9,6,5]
c=[]
mergesort(a,0,len(a))
print(c)
    

my merge sort algo not working