Python基础-2

目录：

1.列表、元组操作

2.字符串操作

3.字典操作

4.集合操作

5.文件操作

6.字符编码与转码

一、列表、元组操作

定义列表

 names = ['Freeman',"Jack",'Ruby']

通过下标访问列表中的元素，下标从0开始计数

 >>> names[0]
 'Freeman'
 >>> names[2]
 'Ruby'
 >>> names[-1]  #可以倒着取,-1表示最后一个
 'Ruby' 

切片:取多个元素

 >>> names = ["Freeman","Tlan","Eric","Rain","Tom","Amy"]
 >>> names[1:4]  #取下标1至下标4之间的数字，包括1，不包括4
 ['Tlan', 'Eric', 'Rain']
 >>> names[1:-1] #取下标1至-1的值，不包括-1
 ['Tlan', 'Eric', 'Rain', 'Tom']
 >>> names[0:3]
 ['Freeman', 'Tlan', 'Eric']
 >>> names[:3] #如果是从头开始取，0可以忽略，跟上句效果一样
 ['Freeman', 'Tlan', 'Eric']
 >>> names[3:] #如果想取最后一个，必须不能写-1，只能这么写
 ['Rain', 'Tom', 'Amy']
 >>> names[3:-1] #这样-1就不会被包含了
 ['Rain', 'Tom']
 >>> names[0::2] #后面的2是代表，每隔一个元素，就取一个
 ['Freeman', 'Eric', 'Tom']
 >>> names[::2] #和上句效果一样
 ['Freeman', 'Eric', 'Tom']

追加

 >>> names
 ['Freeman', 'Tlan', 'Eric', 'Rain', 'Tom', 'Amy']
 >>> names.append("我是新来的")
 >>> names
 ['Freeman', 'Tlan', 'Eric', 'Rain', 'Tom', 'Amy', '我是新来的']

插入

 >>> names
 ['Freeman', 'Tlan', 'Eric', 'Rain', 'Tom', 'Amy', '我是新来的']
 >>> names.insert(2,"强行从Eric前面插入")
 >>> names
 ['Freeman', 'Tlan', '强行从Eric前面插入', 'Eric', 'Rain', 'Tom', 'Amy', '我是新来的']

 >>> names.insert(5,"从eric后面插入试试新姿势")
 >>> names
 ['Freeman', 'Tlan', '强行从Eric前面插入', 'Eric', 'Rain', '从eric后面插入试试新姿势', 'Tom', 'Amy', '我是新来的']

修改

 >>> names
 ['Freeman', 'Tlan', '强行从Eric前面插入', 'Eric', 'Rain', '从eric后面插入试试新姿势', 'Tom', 'Amy', '我是新来的']
 >>> names[2] = "该换人了"
 >>> names
 ['Freeman', 'Tlan', '该换人了', 'Eric', 'Rain', '从eric后面插入试试新姿势', 'Tom', 'Amy', '我是新来的']

删除

 >>> del names[2]
 >>> names
 ['Freeman', 'Tlan', 'Eric', 'Rain', '从eric后面插入试试新姿势', 'Tom', 'Amy', '我是新来的']
 >>> del names[4]
 >>> names
 ['Freeman', 'Tlan', 'Eric', 'Rain', 'Tom', 'Amy', '我是新来的']
 >>>
 >>> names.remove("Eric") #删除指定元素
 >>> names
 ['Freeman', 'Tlan', 'Rain', 'Tom', 'Amy', '我是新来的']
 >>> names.pop() #删除列表最后一个值
 '我是新来的'
 >>> names
 ['Freeman', 'Tlan', 'Rain', 'Tom', 'Amy']

延伸/扩展

 >>> names
 ['Freeman', 'Tlan', 'Rain', 'Tom', 'Amy']
 >>> b = [1,2,3]
 >>> names.extend(b)
 >>> names
 ['Freeman', 'Tlan', 'Rain', 'Tom', 'Amy', 1, 2, 3]

拷贝

 import copy
 a = ['qq','ww','ee',['gg','bb']]
 b = copy.copy(a)
 c = copy.deepcopy(a)
 print(b)
 a[0] = 'New'
 print(a)
 print(b)
 a[3][0] = 'Big'
 print(a)
 print("copy",b)
 print("deepcopy",c)

 结果：
 ['qq', 'ww', 'ee', ['gg', 'bb']]
 ['New', 'ww', 'ee', ['gg', 'bb']]
 ['qq', 'ww', 'ee', ['gg', 'bb']]
 ['New', 'ww', 'ee', ['Big', 'bb']]
 copy ['qq', 'ww', 'ee', ['Big', 'bb']]
 deepcopy ['qq', 'ww', 'ee', ['gg', 'bb']]

统计

 >>> names
 ['Freeman', 'Tlan', 'Amy', 'Tom', 'Amy', 1, 2, 3]
 >>> names.count("Amy")
 2

排序and翻转

 >>> names
 ['Freeman', 'Tlan', 'Amy', 'Tom', 'Amy', 1, 2, 3]
 >>> names.sort() #排序
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
 TypeError: unorderable types: int() < str()   #3.0里不同数据类型不能放在一起排序
 >>> names[-3] = ''
 >>> names[-2] = ''
 >>> names[-1] = ''
 >>> names
 ['Freeman', 'Tlan', 'Amy', 'Tom', 'Amy', '', '', '']
 >>> names.sort()
 >>> names
 ['', '', '', 'Amy', 'Amy', 'Freeman', 'Tlan', 'Tom']

 >>> names.reverse() #反转
 >>> names
 ['Tom', 'Tlan', 'Freeman', 'Amy', 'Amy', '', '', '']

获取列表下表

 >>> names
 ['Tom', 'Tlan', 'Freeman', 'Amy', 'Amy', '', '', '']
 >>> names.index("Amy")
 3 #只返回找到的第一个下标

元组

元组跟列表差不多，也是存一组数，只不是它一旦创建，便不能再修改，所以又叫只读列表

语法

 names = ("Freeman","jack","eric")

元组只有2个方法，一个是count,一个是index。

二、字符串操作

特性：不可修改

 name = 'jack lee'
 name.capitalize()  首字母大写
 name.casefold()   大写全部变小写
 name.center(50,"-")  输出 '---------------------jack lee----------------------'
 name.count('lee') 统计 lee出现次数
 name.encode()  将字符串编码成bytes格式
 name.endswith("lee")  判断字符串是否以 lee结尾
  "jack\tlee".expandtabs(10) 输出'jack      lee'， 将\t转换成多长的空格
  name.find('a')  查找a,找到返回其索引， 找不到返回-1 

 format :
     >>> msg = "my name is {}, and age is {}"
     >>> msg.format("freeman",22)
     'my name is freeman, and age is 22'
     >>> msg = "my name is {1}, and age is {0}"
     >>> msg.format("freeman",22)
     'my name is 22, and age is freeman'
     >>> msg = "my name is {name}, and age is {age}"
     >>> msg.format(age=22,name="free")
     'my name is free, and age is 22'
 format_map
     >>> msg.format_map({'name':'freeman','age':22})
     'my name is alex, and age is 22'

 msg.index('a')  返回a所在字符串的索引
 '9aA'.isalnum()   True

 ''.isdigit() 是否整数
 name.isnumeric
 name.isprintable
 name.isspace
 name.istitle
 name.isupper
  "-".join(['freeman','jack','rain'])
 'freeman-jack-rain'

 maketrans
     >>> intab = "aeiou"  #This is the string having actual characters.
     >>> outtab = "" #This is the string having corresponding mapping character
     >>> trantab = str.maketrans(intab, outtab)
     >>>
     >>> str = "this is string example....wow!!!"
     >>> str.translate(trantab)
     'th3s 3s str3ng 2x1mpl2....w4w!!!'

  msg.partition('is')   输出 ('my name ', 'is', ' {name}, and age is {age}') 

  >>> "alex li, chinese name is lijie".replace("li","LI",1)#LI替换li,1表示替换第一个，如果换成2，就是替换前两个
      'alex LI, chinese name is lijie'

  msg.swapcase 大小写互换

  >>> msg.zfill(40)
 '00000my name is {name}, and age is {age}'

 >>> n4.ljust(40,"-")
 'Hello 2orld-----------------------------'
 >>> n4.rjust(40,"-")
 '-----------------------------Hello 2orld'

 >>> b="ddefdsdff_哈哈"
 >>> b.isidentifier() #检测一段字符串可否被当作标志符，即是否符合变量命名规则
 True

三、字典操作

字典一种key - value 的数据类型。

语法：

 info = {
     'stu001': "Xiao Ming",
     'stu002': "Xiao Hong",
     'stu003': "Xiao Gou",
 }

字典的特性：

• dict是无序的
• key必须是唯一的，因此字典天生去重复性

增加

 info["stu004"] = "苍井空"

 {'stu001': 'Xiao Ming',
  'stu002': 'Xiao Hong',
  'stu003': 'Xiao Gou',
  'stu004': '苍井空'}

修改

 info['stu001'] = 'Freeman'

 {'stu001': 'Freeman',
  'stu002': 'Xiao Hong',
  'stu003': 'Xiao Gou',
  'stu004': '苍井空'}

删除

 >>> info
 {'stu001': 'Freeman',
  'stu002': 'Xiao Hong',
  'stu003': 'Xiao Gou',
  'stu004': '苍井空'}
 >>> info.pop("stu001") #标准删除姿势
  'Freeman'
 >>> info
 {'stu002': 'Xiao Hong', 'stu003': 'Xiao Gou', 'stu004': '苍井空'}
 >>> del info['stu003'] #换个姿势删除
 >>> info
 {'stu002': 'Xiao Hong', 'stu004': '苍井空'}
 >>>
 >>> info
 {'stu002': 'Xiao Hong', 'stu004': '苍井空'} #随机删除
 >>> info.popitem()
 ('stu002', 'Xiao Hong')
 >>> info
  {'stu004': '苍井空'}

查找

 >>> info = {'stu002': 'Xiao Hong', 'stu003': 'Xiao Gou'}
 >>>
 >>> "stu002" in info #标准用法
 True
 >>> info.get("stu002")  #获取
 'Xiao Hong'
 >>> info["stu002"] #同上，但是看下面
 'Xiao Hong'
 >>> info["stu005"]  #如果一个key不存在，就报错，get不会，不存在只返回None
 Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
 KeyError: 'stu1105'

其他

 #values
 >>> info.values()
 dict_values(['Xiao Hong', 'Xiao Gou'])

 #keys
 >>> info.keys()
 dict_keys(['stu002', 'stu003'])

 #setdefault
 >>> info.setdefault("stu006","Freeman")
 'Freeman'
 >>> info
 {'stu002': 'Xiao Hong', 'stu003': 'Xiao Gou', 'stu006': 'Freeman'}
 >>> info.setdefault("stu002","why")
 'Xiao Hong'
 >>> info
 {'stu002': 'Xiao Hong', 'stu003': 'Xiao Gou', 'stu006':'Freeman'}

 #update
 >>> info
 {'stu002': 'Xiao Hong', 'stu003': 'Xiao Gou', 'stu006':'Freeman'}
 >>> b = {1:2,3:4, "stu002":"龙泽萝拉"}
 >>> info.update(b)
 >>> info
 {'stu006': 'Freeman', 1: 2, 'stu002': '龙泽萝拉', 3: 4, 'stu003': 'Xiao Gou'}

 #items
 info.items()
 dict_items([('stu006', 'Freeman'), (1, 2), ('stu002', '龙泽萝拉'), (3, 4), ('stu003', 'Xiao Gou')])

 #通过一个列表生成默认dict,有个没办法解释的坑，少用吧这个
 >>> dict.fromkeys([1,2,3],'testd')
 {1: 'testd', 2: 'testd', 3: 'testd'}

循环dict

 #方法1
 for key in info:
     print(key,info[key])

 #方法2
 for k,v in info.items(): #会先把dict转成list,数据量大时莫用
     print(k,v)

四、集合操作

集合是一个无序的，不重复的数据组合，它的主要作用如下：

• 去重，把一个列表变成集合，就自动去重了
• 关系测试，测试两组数据之前的交集、差集、并集等关系

常用操作

 s = set([3,5,9,10])      #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 

五、文件操作

对文件操作流程

1. 打开文件，得到文件句柄并赋值给一个变量
2. 通过句柄对文件进行操作
3. 关闭文件

现有文件如下

 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

基本操作

 f = open('lyrics') #打开文件
 first_line = f.readline()
 print('first line:',first_line) #读一行
 print('我是分隔线'.center(50,'-'))
 data = f.read()# 读取剩下的所有内容,文件大时不要用
 print(data) #打印文件

 f.close() #关闭文件

打开文件的模式有：

• r，只读模式（默认）。
• w，只写模式。【不可读；不存在则创建；存在则删除内容；】
• a，追加模式。【可读；   不存在则创建；存在则只追加内容；】

"+" 表示可以同时读写某个文件

• r+，可读写文件。【可读；可写；可追加】
• w+，写读
• a+，同a

"U"表示在读取时，可以将 \r \n \r\n自动转换成 \n （与 r 或 r+ 模式同使用）

• rU
• r+U

"b"表示处理二进制文件（如：FTP发送上传ISO镜像文件，linux可忽略，windows处理二进制文件时需标注）

• rb
• wb
• ab

其它语法

 def close(self): # real signature unknown; restored from __doc__
         """
         Close the file.

         A closed file cannot be used for further I/O operations.  close() may be
         called more than once without error.
         """
         pass

     def fileno(self, *args, **kwargs): # real signature unknown
         """ Return the underlying file descriptor (an integer). """
         pass

     def isatty(self, *args, **kwargs): # real signature unknown
         """ True if the file is connected to a TTY device. """
         pass

     def read(self, size=-1): # known case of _io.FileIO.read
         """
         注意，不一定能全读回来
         Read at most size bytes, returned as bytes.

         Only makes one system call, so less data may be returned than requested.
         In non-blocking mode, returns None if no data is available.
         Return an empty bytes object at EOF.
         """
         return ""

     def readable(self, *args, **kwargs): # real signature unknown
         """ True if file was opened in a read mode. """
         pass

     def readall(self, *args, **kwargs): # real signature unknown
         """
         Read all data from the file, returned as bytes.

         In non-blocking mode, returns as much as is immediately available,
         or None if no data is available.  Return an empty bytes object at EOF.
         """
         pass

     def readinto(self): # real signature unknown; restored from __doc__
         """ Same as RawIOBase.readinto(). """
         pass #不要用,没人知道它是干嘛用的

     def seek(self, *args, **kwargs): # real signature unknown
         """
         Move to new file position and return the file position.

         Argument offset is a byte count.  Optional argument whence defaults to
         SEEK_SET or 0 (offset from start of file, offset should be >= 0); other values
         are SEEK_CUR or 1 (move relative to current position, positive or negative),
         and SEEK_END or 2 (move relative to end of file, usually negative, although
         many platforms allow seeking beyond the end of a file).

         Note that not all file objects are seekable.
         """
         pass

     def seekable(self, *args, **kwargs): # real signature unknown
         """ True if file supports random-access. """
         pass

     def tell(self, *args, **kwargs): # real signature unknown
         """
         Current file position.

         Can raise OSError for non seekable files.
         """
         pass

     def truncate(self, *args, **kwargs): # real signature unknown
         """
         Truncate the file to at most size bytes and return the truncated size.

         Size defaults to the current file position, as returned by tell().
         The current file position is changed to the value of size.
         """
         pass

     def writable(self, *args, **kwargs): # real signature unknown
         """ True if file was opened in a write mode. """
         pass

     def write(self, *args, **kwargs): # real signature unknown
         """
         Write bytes b to file, return number written.

         Only makes one system call, so not all of the data may be written.
         The number of bytes actually written is returned.  In non-blocking mode,
         returns None if the write would block.
         """
         pass

with语句

为了避免打开文件后忘记关闭，可以通过管理上下文，即：

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

如此方式，当with代码块执行完毕时，内部会自动关闭并释放文件资源。

在Python 2.7 后，with又支持同时对多个文件的上下文进行管理，即：

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

六、字符编码与转码

1.在python2默认编码是ASCII，python3里默认是unicode；

2.unicode 分为 utf-32(占4个字节),utf-16(占两个字节)，utf-8(占1-4个字节)， 因此，utf-16就是现在最常用的unicode版本， 不过在文件里存的还是utf-8，因为utf-8省空间；

3.在py3中encode，在转码的同时还会把string 变成bytes类型，decode在解码的同时还会把bytes变回string。

上图仅适用于python2

 #-*-coding:utf-8-*-

 import sys
 print(sys.getdefaultencoding())

 msg = "我爱北京天安门"
 msg_gb2312 = msg.decode("utf-8").encode("gb2312")
 gb2312_to_gbk = msg_gb2312.decode("gbk").encode("gbk")

 print(msg)
 print(msg_gb2312)
 print(gb2312_to_gbk)

Python2

 #-*-coding:gb2312 -*-   #这个也可以去掉

 import sys
 print(sys.getdefaultencoding())

 msg = "我爱北京天安门"
 #msg_gb2312 = msg.decode("utf-8").encode("gb2312")
 msg_gb2312 = msg.encode("gb2312") #默认就是unicode,不用再decode,喜大普奔
 gb2312_to_unicode = msg_gb2312.decode("gb2312")
 gb2312_to_utf8 = msg_gb2312.decode("gb2312").encode("utf-8")

 print(msg)
 print(msg_gb2312)
 print(gb2312_to_unicode)
 print(gb2312_to_utf8)

Python3