s = set([1,4,5,7,3,8,7,9,6])      #创建一个数值集合  

 t = set("Hello")         #创建一个唯一字符的集合  

 a = t | s          # t 和 s的并集  

 b = t & s          # t 和 s的交集  

 c = t – s          # 求差集（项在t中，但不在s中）  

 d = t ^ s          # 对称差集（项在t或s中，但不会同时出现在二者中）  

 基本操作：  

 t.add('x')            # 添加一项  

 s.update([10,37,42])  # 在s中添加多项  

 使用remove()可以删除一项：  

 t.remove('H')  

 len(s)

 set 的长度  

 x in s

 测试 x 是否是 s 的成员  

 x not in s

 测试 x 是否不是 s 的成员  

 s.issubset(t)

 s <= t

 测试是否 s 中的每一个元素都在 t 中  

 s.issuperset(t)

 s >= t

 测试是否 t 中的每一个元素都在 s 中  

 s.union(t)

 s | t

 返回一个新的 set 包含 s 和 t 中的每一个元素  

 s.intersection(t)

 s & t

 返回一个新的 set 包含 s 和 t 中的公共元素  

 s.difference(t)

 s - t

 返回一个新的 set 包含 s 中有但是 t 中没有的元素  

 s.symmetric_difference(t)

 s ^ t

 返回一个新的 set 包含 s 和 t 中不重复的元素  

 s.copy()

 返回 set “s”的一个浅复制

 Somehow, it seems the love I knew was always the most destructive kind

 不知为何，我经历的爱情总是最具毁灭性的的那种

 Yesterday when I was young

 昨日当我年少轻狂

 The taste of life was sweet

 生命的滋味是甜的

 As rain upon my tongue

 就如舌尖上的雨露

 I teased at life as if it were a foolish game

 我戏弄生命 视其为愚蠢的游戏

 The way the evening breeze

 就如夜晚的微风

 May tease the candle flame

 逗弄蜡烛的火苗

 The thousand dreams I dreamed

 我曾千万次梦见

 The splendid things I planned

 那些我计划的绚丽蓝图

 I always built to last on weak and shifting sand

 但我总是将之建筑在易逝的流沙上

 I lived by night and shunned the naked light of day

 我夜夜笙歌 逃避白昼赤裸的阳光

 And only now I see how the time ran away

 事到如今我才看清岁月是如何匆匆流逝

 Yesterday when I was young

 昨日当我年少轻狂

 So many lovely songs were waiting to be sung

 有那么多甜美的曲儿等我歌唱

 So many wild pleasures lay in store for me

 有那么多肆意的快乐等我享受

 And so much pain my eyes refused to see

 还有那么多痛苦 我的双眼却视而不见

 I ran so fast that time and youth at last ran out

 我飞快地奔走 最终时光与青春消逝殆尽

 I never stopped to think what life was all about

 我从未停下脚步去思考生命的意义

 And every conversation that I can now recall

 如今回想起的所有对话

 Concerned itself with me and nothing else at all

 除了和我相关的 什么都记不得了

 The game of love I played with arrogance and pride

 我用自负和傲慢玩着爱情的游戏

 And every flame I lit too quickly, quickly died

 所有我点燃的火焰都熄灭得太快

 The friends I made all somehow seemed to slip away

 所有我交的朋友似乎都不知不觉地离开了

 And only now I'm left alone to end the play, yeah

 只剩我一个人在台上来结束这场闹剧

 Oh, yesterday when I was young

 噢 昨日当我年少轻狂

 So many, many songs were waiting to be sung

 有那么那么多甜美的曲儿等我歌唱

 So many wild pleasures lay in store for me

 有那么多肆意的快乐等我享受

 And so much pain my eyes refused to see

 还有那么多痛苦 我的双眼却视而不见

 There are so many songs in me that won't be sung

 我有太多歌曲永远不会被唱起

 I feel the bitter taste of tears upon my tongue

 我尝到了舌尖泪水的苦涩滋味

 The time has come for me to pay for yesterday

 终于到了付出代价的时间 为了昨日

 When I was young

 当我年少轻狂

yesterday

 f = open("yesterday","r",encoding="utf-8")

 first_line = f.readline()

 print("read first line:",first_line)

 print("我是分割线".center(50,'-'))  #打印内容居中，其他‘-’

 d = f.read()  #读取文件中剩余内容

 print(d)

 f.close()

 #w模式是已写打开文件，实质是创建一个文件，因此会覆盖原文件

 f = open("yesterday3","w",encoding="utf-8")

 f.write("为了不覆盖，\n重新建立")

 f = open("yesterday3","a",encoding="utf-8")

 f.write("我是新的数据,\n来读取我看看")

 f.close()

 #读文件前5行

 f = open("yesterday","r",encoding="utf-8")

 for i in range(5):

     print(f.readline().strip())

 #读取全部文件，到第十行就结束

 f = open("yesterday","r",encoding="utf-8")

 for index,line in enumerate(f.readlines()):

     if index == 9:

         print("-----我是分割线-----")

         break

     print(index,line.strip())

 f = open("yesterday","r",encoding="utf-8")

 count = 0

 for line in f:    #文件逐行读取，效率最高，此时line已不为列表，需要重新计数

     if count == 9:

         print("---我是分割线---")

         count +=1

         break

     print(line.strip())

     count +=1

 f = open("yesterday","r",encoding="utf-8")

 print(f.tell())

 print(f.readline().strip())

 print(f.tell())

 f = open("yesterday","r",encoding="utf-8")

 print(f.tell())

 print(f.readline().strip())

 print(f.tell())

 f.seek(0)

 print(f.tell())

 f = open("yesterday","r",encoding="utf-8")

 print(f.encoding)

 f = open("yesterday","r",encoding="utf-8")

 print(f.fileno())

 >>> f = open("yesterday2","w",encoding="utf-8")

 #这时'hello word'在缓存中

 >>> f.write("hello word")

 10

 #强刷到磁盘上

 >>> f.flush()

 import sys,time

 for i in range(50):

     sys.stdout.write(">")

     sys.stdout.flush()

     time.sleep(0.5)

 #文件中内容替换

 f = open("yesterday3","r",encoding="utf-8")

 f_new = open("yesterday3.bak","w",encoding="utf-8")

 for line in f:

     if "我是第十行" in line:

         line = line.replace("我是第十行","今天是星期二")

     f_new.write(line)

 f.close()

 f_new.close()

 with open('log','r') as f:

 with open('log1') as obj1, open('log2') as obj2:

     pass