Python-《twinkle twinkle little star》统计单词出现次数

统计英文儿歌《twinkle twinkle little star》中，使用到的单词及其出现次数。要求去除单词大小写的影响，不统计标点符号的个数，并按降序输出。
Twinkle, twinkle, little star,
How I wonder what you are!
Up above the world so high,
Like a diamond in the sky.
Twinkle, twinkle, little star,
How I wonder what you are!
When the blazing sun is gone,
When he nothing shines upon,
Then you show your little light,
Twinkle, twinkle, all the night.
Twinkle, twinkle, little star,
How I wonder what you are!

song = """Twinkle, twinkle, little star,
How I wonder what you are!
Up above the world so high,
Like a diamond in the sky.
Twinkle, twinkle, little star,
How I wonder what you are!
When the blazing sun is gone,
When he nothing shines upon,
Then you show your little light,
Twinkle, twinkle, all the night.
Twinkle, twinkle, little star,
How I wonder what you are!
"""
lines = song.lower().strip()\
    .replace(",","").replace(".",'').replace("!",'').replace("?",'').split("\n")
words = []
word_counts={}
for line in lines:
    words += line.split(" ")
for word in words:
    if word in word_counts:
        word_counts[word] = word_counts[word] + 1
    else:
        word_counts[word] = 1
word_key_count = []
for key in word_counts:
    key_count = [key, word_counts[key]]
    word_key_count.append(key_count)
#冒泡排序
for index in range(1,len(word_key_count)):
    for sub_index in range(index,0,-1):
        if word_key_count[sub_index][1] > word_key_count[sub_index - 1][1]:
            temp = word_key_count[sub_index - 1]
            word_key_count[sub_index - 1] = word_key_count[sub_index]
            word_key_count[sub_index] = temp
for index in range(len(word_key_count)):
    print(word_key_count[index][0],word_key_count[index][1])