字符串的函数应用

Emma Woodhouse, handsome, clever, and rich, with a comfortable home and happy disposition, seemed to unite some of the best blessings of existence; and had lived nearly twenty-one years in the world with very little to distress or vex her.

针对上述语料，请完成以下操作:

(1) 统计上述文本中共有多少个单词：

a = "Emma Woodhouse, handsome, clever, and rich, with a comfortable home and happy disposition, seemed to unite some of the best blessings of existence; and had lived nearly twenty-one years in the world with very little to distress or vex her."
b = a.replace(',','')
c = b.replace('.','')  #替掉（或者说是删除掉）逗号和句号，为下一步进入列表的规范化做准备（其实是为了第二问做准备）
d = c.split(' ')  #空格分隔单词输入列表
print(len(d))  #输出列表元素数量

(2) 输出上述文本中所有长度为4个字母的单词：

list_i = []  #先预设一个空列表
for i in d:
    if len(i) == 4:
        list_i.append(i)  #经典的列表遍历，查找长度并将查找结果输入新列表
print(list_i)

(3) 将上一步输出的单词分别以首字母大写、全大写、全小写的方式输出：

for word in list_i:
    print(word.title(),word.upper(),word.lower())  #毋庸多言

这样上传一下云端，顺便分享一波，还望指教。