英文词频统计预备，组合数据类型练习

1.实例: 下载一首英文的歌词或文章，将所有,.？！等替换为空格，将所有大写转换为小写，统计某几个单词出现的次数，分隔出一个一个的单词。

song='''I messed up tonight, I lost another fight
I still mess up but I'll just start again
I keep falling down, I keep on hitting the ground
I always get up now to see what's next
Birds don't just fly, they fall down and get up
Nobody learns without getting it won
I won't give up, no I won't give in
Til I reach the end, then I'll start again
No I won't leave, I wanna try everything
I wanna try even though I could fail
I won't give up, no I won't give in
Til I reach the end and then I'll start again
No I won't leave, I wanna try everything
I wanna try even though I could fail'''
song=song.lower()
for i in ',':
    song=song.replace(i,' ')
print(song)
words=song.split(' ')
print(words)

2.列表实例：由字符串创建一个作业评分列表，做增删改查询统计遍历操作。例如，查询第一个3分的下标，统计1分的同学有多少个，3分的同学有多少个等。

grades=list('12313561325')
for i in range(len(grades)):
    grades[i]=int(grades[i])
print(grades)
print(grades.index(3))
print(grades.count(1))
print(grades.count(3))

3.简要描述列表与元组的异同。

 答：列表和元组非常类似，有时候他们都干一样的事情。但他们最大的区别是元组一旦被赋值，值不可以被改变，一旦改变就会出错；但是列表可以任意的更改。其次的区别是他们用不同的符号表示，复制的时候，列表用方括号[]，而元组用小括号（）。