组合数据类型，英文词频统计

练习：

• 总结列表，元组，字典，集合的联系与区别。
• 列表，元组，字典，集合的遍历。

列表，元组，字典是有顺序的，而集合是没顺序的

列表是以方括号形式表示，元组是以圆括号表示，字典以花括号表示，集合则是以[()]的形式表示

列表是可变对象,它支持在原处修改的操作.也可以通过指定的索引和分片获取元素。区别于元组，可动态增加，删除，更新。

元组和列表在结构上没有什么区别，唯一的差异在于元组是只读的，不能修改。元组用“()”表示。元组一旦定义其长度和内容都是固定的。一旦创建元组，则这个元组就不能被修改，即不能对元组进行更新、增加、删除操作。若想创建包含一个元素的元组，则必须在该元素后面加逗号“,”，否则创建的不是一个元组，而是一个字符串。

集合没有特殊的表示方法，而是通过一个set函数转换成集合。集合是一个无序不重复元素集，基本功能包括关系测试和消除重复元素.。

字典最大的价值是查询，通过键，查找值。

 

英文词频统计：

• 下载一首英文的歌词或文章str
• 分隔出一个一个的单词 list
• 统计每个单词出现的次数 dict

strlrc = '''Need You Now - Lady Antebellum
Picture perfect memories
Scattered all around the floor
Reaching for the phone cause
I can't fight it any more
And I wonder if I ever cross your mind
For me it happens all the time
It's a quarter after one
I'm all alone
and I need you now
Said I wouldn't call
but I lost all control
and I need you now
And I don't know
how I can do without
I just need you now
Another shot of whiskey
can't stop looking at the door
Wishing you'd come sweeping
in the way you did before
And I wonder if
I ever cross your mind
For me it happens all the time
It's a quarter after one
I'm a little drunk
And I need you now
Said I wouldn't call
but I lost all control
and I need you now
And I don't know
how I can do without
I just need you now
Yes I'd rather hurt
than feel nothing at all
It's a quarter after one
I'm all alone
and I need you now
And I said I wouldn't call
but I'm a little drunk
and I need you now
And I don't know
how I can do without
I just need you now
I just need you now
Oh baby I need you now

'''

strList = strlrc.split()
strSet = set(strList)

strDict = {}
for word in strSet:
    strDict[word] = strList.count(word)
print(len(strDict), strDict)