python3 对一个句子从尾到头输出且对其中长度小于某值的词语进行倒序

#所有句子整体倒序，对长度小于某值的再倒序
def spin_words(a):
    lenth = len(a)
    # print(len(a))
    b = []
    c=[]
    for i in range(lenth):
        if a[i] == " ":
            b.append(i)  # 定位出空格所在位置前一个字符位置
    b.append(lenth)
    b=b[::-1]
    # print(b)

    if len(b)==1:
        c=a[::-1]
    else:
        for j in range(len(b)):
            if b[j] == b[-1]:
                if b[j] <= 5:
                    temp = a[:b[j] + 1][::-1]  # 包含右空格
                else:
                    temp = a[:b[j]]
                temp = temp +" "
            elif b[j] == b[0]:
                d = b[j] - b[j + 1] - 1
                if d <= 5:
                    temp = a[b[j + 1] + 1:b[j] + 1][::-1]  # 前闭后开，不包含左空格，包含右空格
                else:
                    temp = a[b[j + 1] + 1:b[j] + 1]
            else:
                d = b[j] - b[j + 1] - 1
                if d <= 5:
                    temp = a[b[j + 1]:b[j] + 1][::-1]
                else:
                    temp = a[b[j + 1]:b[j] + 1]
            c.append(temp)
        c="".join(c)
    return c

a='i love my family'
print(a)
print(spin_words(a))

> i love my family
  family ym  evol  i