Python运维开发之路《文件处理》

一、python字典操作

1.字典的定义

　　字典一种key-value的数据类型，类似于json串。

2.字典的特性

key:value
字典不可变，key唯一

key的定义规则：
1.不可变，数字、字符串、字典、元组(定义符合()，与列表完全一致，唯一不同的是元组内元素不可变)
2.key必须是唯一的,所以字典天生有去重功能

value的定义规则：
1.任意数据类型

3.字典的使用方法

　　字典的增、删、改、查

查询:
print(dic['name'])
print(dic.get('name'))    #get方法查询不存在的项不会报错

添加:
dic['gender'] = 'female'    #k:v 无序添加

修改:
dic['name'] = '11'  #key不可修改

删除:
del     #万能删除
del dic['name'] #删除key

　　其他使用方法和函数调用

dicl = dict.fromkeys()  #快速生成字典
dic.copy()          #浅拷贝，只拷贝一层
dic.get()           #值不存在不会报错
dic.items()         #打印转换为列表形式
dic.keys()          #取出字典中所有的key值
dic.pop()           #pop删除，括号内写key，key不存在会报错
dic.popitem()       #随机删除一对key.val
dic.setdefault()    #添加字典
dic.update()        #添加新字典，添加字典内容，修改字典内容
dic.values()        #取出字典所有values值

 　　字典的定义方法

字典的定义方法：
dic = dict()                            #空字典
dic1 = dict({'name':'alex','age':18})
print(dic1)
dic2 = dict(name='alex',age=18)
print(dic2)
dic3 = dict((('name','alex'),('age','18')))
print(dic3)

二、集合

1.集合的介绍　

　　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

2.集合的操作方法

增加      add        #添加元素到集合
         update      #添加集合到集合

随机删除    pop       #随机删除
           remove    #指定删除，如果删除元素不存在，程序报错
           discard   #指定删除，如果删除元素不存在，报none

清空
        clear       #清空

差集并赋值
        symmetric_difference_update #差集后，赋予新值

　　集合的几种模式

- 交集：intersection    print(s1&s2)
- 并集：union       print(s1|s2)
- 差集：difference  print(s1-s2)        
- 子集：issubset    print(s1<=s2)
- 父集：issuperset  print(s1>=s2)
- 对称差集：symmetric_difference    print(s1^s2)    #去掉两个集合里重复的

三、字符编码

1.在python2默认编码是ASCII, python3里默认是utf-8

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-8就是unicode

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

4.内存固定使用Unicode编码，硬盘的编码可以修改(即可以修改的软件编码)

5.使用什么编码往硬盘存，就用什么编码去读

6.程序运行分两个阶段：

　　- 从硬盘读到内存

　　- python解释器运行读到内存里的代码

7.针对.py文件，python与nodpad++\vim的区别是多了运行已经读到内存里的代码

四、python文件处理

1.关于python循环读取数据

文本文件：

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

读取文件前5行：

#-*- coding:utf-8 -*-
data = open("lyrics",encoding='UTF-8')

##循环打印readlines,占用内存空间不推荐
for index,line in enumerate(data.readlines()):
    if index < 5:
        print(line)
    else:
        break

##循环打印readline
for i in range(5):
    print(data.readline().strip())

##循环打印for
count = 0
for line in data:
    if count < 5:
        print(line.strip())
        count +=1
    else:
        break

 2.python文件处理命令用法

基本的文件模式

#r,读模式，open命令默认是读模式
f = open('testfile','r',encoding='utf-8')
print(f.read())

#w,写模式
f = open('testfile','w',encoding='utf-8')
f.write('人生苦短，我学python\n')
f.close()

#a,追加模式
f = open('testfile','a',encoding='utf-8')
f.write('我呵呵你！\n')
f.close()

#删除，打开一个文件写入空即删除
f = open('testfile','r+',encoding='utf-8')
f.readline()
f.write('')

#r+,读写 可读，追加内容到最后
f = open('testfile','r+',encoding='utf-8')
f.readline()
f.write('devops\n')

#w+,写读  新建文件，写入再读取
f = open('testfile','w+',encoding='utf-8')
f.readline()
f.write('devops2\n')

# a+,追加读 清空源文件，再添加，然后读取
f = open('testfile','w+',encoding='utf-8')
f.readline()
f.write('devops3\n')

其他文件操作方法

f = open('testfile','w+',encoding='utf-8')
f.close()

f.closed    #判断操作的文件是否关闭
f.encoding  #打印文件的编码格式
f.fileno()  #返回操作系统接口文件索引<网络编程，I/O复用>
f.flush()   #刷新操作
f.isatty()  #判断打开的文件是否是终端文件
f.name      #打印文件名
f.newlines  #未读取到行分隔符时为 None,只有一种行分隔符时为一个字符串,当文件有多种类型的行结束符时,则为一个包含所有当前所遇到的行结束符的列表
f.readable()    #同isatty类似
f.seek()    #移动光标，到固定位置返回此位置以后的内容(按照字符移)
f.tell()    #打印光标所在位置的索引
f.truncate()    #截断，配合seek，括号内指定保留字符数量，从头开始切
f.writelines()  #写列表到文件

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