1.字典实例：建立学生学号成绩字典，做增删改查遍历操作。
dic={"aa":"90","bb":"91","cc":"92","dd":"94","ee":"95"}
print("查询aa的成绩")
print(dic.get('aa'))
print("删除bb成绩")
dic.pop('bb')
print("bb的成绩:","bb" in dic,"不存在")
print("aa成绩改为80")
dic['aa']=80
print(dic.items())
print("添加gg的成绩")
dic["gg"]="99"
print(dic)
print("所有学生名单:")
for i in dic:
print(i)
print("所有学生成绩:")
for i in dic:
print(i,dic[i])
查询aa的成绩 90 删除bb成绩 bb的成绩: False 不存在 aa成绩改为80 dict_items([('aa', 80), ('cc', '92'), ('dd', '94'), ('ee', '95')]) 添加gg的成绩 {'aa': 80, 'cc': '92', 'dd': '94', 'ee': '95', 'gg': '99'} 所有学生名单: aa cc dd ee gg 所有学生成绩: aa 80 cc 92 dd 94 ee 95 gg 99
2.列表，元组，字典，集合的遍历。
lis=["1","2","3","4"]
tu=("4","5")
dic={"1":"91","2":"92","3":"93","4":"94"}
s=set(lis)
print("列表")
for i in lis:
print(i)
print("元组")
for i in tu:
print(i)
print("字典")
for i in dic:
print(i,dic[i])
print("set")
for i in s:
print(i)
列表
1
2
3
4
元组
4
5
字典
1 91
2 92
3 93
4 94
set
3
2
1
总结列表，元组，字典，集合的联系与区别：
（1）列表是任意对象的序列。列表用方括号表示。
（2）将一组值打包到一个对象中，称为元组。元组用圆括号表示。元组和列表的大部分操作相同。但是，列表是不固定的，可以随时插入，删除；而元组一旦确认就不能够再更改。所以，系统为了列表的灵活性，就需要牺牲掉一些内存；而元组就更为紧凑。
（3）与列表和元组不同，集合是无序的，也不能通过索引进行访问。此外，集合中的元素不能重复。
（4）字典就是一个关联数组或散列表，其中包含通过关键字索引的对象。用大括号表示。与集合相比，通过关键字索引，所以比集合访问方便。字典是Python解释器中最完善的数据类型。
3.英文词频统计实例
A. 待分析字符串
B. 分解提取单词
a. 大小写 txt.lower() b. 分隔符'.,:;?!-_’ c.单词列表
s='''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! Then the traveler in the dark Thanks you for your tiny spark; He could not see which way to go, If you did not twinkle so. Twinkle, twinkle, little star, How I wonder what you are! Twinkle Twinkle Little Star''' s=s.lower() print('大写转换为小写:'+s) for i in ',.!': s=s.replace(i,' ') print('所有标点符号替换为空格：'+s) print('单词列表及词频：') words=s.split(' ') dic={} words.sort() disc=set(words) for i in disc: dic[i] = 0 for i in words: dic[i] = dic[i]+1 items = dic.items() print(items)
大写转换为小写: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! then the traveler in the dark thanks you for your tiny spark; he could not see which way to go, if you did not twinkle so. twinkle, twinkle, little star, how i wonder what you are! twinkle twinkle little star 所有标点符号替换为空格：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 then the traveler in the dark thanks you for your tiny spark; he could not see which way to go if you did not twinkle so twinkle twinkle little star how i wonder what you are twinkle twinkle little star 单词列表及词频： dict_items([('', 10), ('shines', 1), ('sky', 1), ('world', 1), ('you', 7), ('twinkle', 8), ('in', 2), ('night', 1), ('upon', 1), ('dark thanks', 1), ('for', 1), ('what', 4), ('your', 2), ('a', 1), (' how', 4), ('so', 2), ('above', 1), ('diamond', 1), ('show', 1), (' if', 1), ('all', 1), ('could', 1), (' when', 2), (' up', 1), ('way', 1), ('nothing', 1), ('high', 1), ('star', 5), ('light', 1), ('spark; he', 1), ('is', 1), ('traveler', 1), ('which', 1), ('wonder', 4), ('did', 1), ('tiny', 1), ('little', 6), (' twinkle', 5), ('go', 1), ('blazing', 1), ('the', 6), ('he', 1), ('i', 4), ('see', 1), ('are', 4), ('not', 2), ('sun', 1), ('to', 1), (' then', 2), (' like', 1), ('gone', 1)])