Mergesort

def merge(e, d):
    r = []
    i, j = 0, 0
    while i < len(e) and j < len(d):
        if e[i] <= d[j]:
            r.append(e[i])
            i += 1
        else:
            r.append(d[j])
            j += 1
    r += e[i:]
    r += d[j:]
    return r
def mergesort(v):
    if len(v) < 2:
        return v
    else:
        m = len(v) // 2
        e = mergesort(v[:m])
        d = mergesort(v[m:])
        return merge(e, d)
print (mergesort([3, 4, 8, 0, 6, 7, 4, 2, 1, 9, 4, 5]))