python 小白(无编程基础，无计算机基础)的开发之路 day2

本节内容

列表、元组操作
字符串操作
字典操作
集合操作
文件操作
字符编码与转码

1. 列表、元组操作

列表是我们最以后最常用的数据类型之一，通过列表可以对数据实现最方便的存储、修改等操作

定义列表

1	`names` `=` `['Alex',"Tenglan",'Eric']`

通过下标访问列表中的元素，下标从0开始计数

>>> names[0]

'Alex'

>>> names[2]

'Eric'

>>> names[-1]

'Eric'

>>> names[-2] #还可以倒着取

'Tenglan'

切片:取多个元素　　

追加

插入

修改

删除

扩展

拷贝

copy真的这么简单么？那我还讲个屁。。。

统计

排序&翻转

获取下标

元组

元组其实跟列表差不多，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

1	`names` `=` `("alex","jack","eric")`

它只有2个方法，一个是count,一个是index，完毕。　　

2. 字符串操作　　　

特性：不可修改　

name.capitalize()  首字母大写
name.casefold()   大写全部变小写
name.center(50,"-")  输出 '---------------------Alex Li----------------------'
name.count('lex') 统计 lex出现次数
name.encode()  将字符串编码成bytes格式
name.endswith("Li")  判断字符串是否以 Li结尾
 "Alex\tLi".expandtabs(10) 输出'Alex      Li'， 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("alex",22)
    'my name is alex, and age is 22'
    >>> msg = "my name is {1}, and age is {0}"
    >>> msg.format("alex",22)
    'my name is 22, and age is alex'
    >>> msg = "my name is {name}, and age is {age}"
    >>> msg.format(age=22,name="ale")
    'my name is ale, and age is 22'
format_map
    >>> msg.format_map({'name':'alex','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

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

maketrans
    >>> intab = "aeiou"  #This is the string having actual characters.
    >>> outtab = "12345" #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)
     '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

3. 字典操作

字典一种key - value 的数据类型，使用就像我们上学用的字典，通过笔划、字母来查对应页的详细内容。

语法:

info = {
    'stu1101': "TengLan Wu",
    'stu1102': "LongZe Luola",
    'stu1103': "XiaoZe Maliya",
}

字典的特性：

dict是无序的
key必须是唯一的,so 天生去重

增加

修改

删除

查找

多级字典嵌套及操作

其它姿势

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,数据里大时莫用
    print(k,v)

三年菜单文艺青年版

4.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

5. 文件操作

对文件操作流程

打开文件，得到文件句柄并赋值给一个变量
通过句柄对文件进行操作
关闭文件

现有文件如下

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）

"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）

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：

1 2	`with` `open('log1') as obj1,` `open('log2') as obj2:` `pass`

程序练习　　

程序1: 实现简单的shell sed替换功能

程序2:修改haproxy配置文件

需求：

需求

原配置文件

6. 字符编码与转码

详细文章:

http://www.cnblogs.com/yuanchenqi/articles/5956943.html

http://www.diveintopython3.net/strings.html

需知:

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)， so 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utf8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py2

in python2

in python3