python归并排序是什么

def merge(s1,s2,s):

    """将两个列表是s1，s2按顺序融合为一个列表s,s为原列表"""

    # j和i就相当于两个指向的位置，i指s1，j指s2

    i = j = 0

    while i+j<len(s):

        # j==len(s2)时说明s2走完了，或者s1没走完并且s1中该位置是最小的

        if j==len(s2) or (i<len(s1) and s1[i]<s2[j]):

            s[i+j] = s1[i]

            i += 1

        else:

            s[i+j] = s2[j]

            j += 1