文件操作以及序列化,python之文件操作

微型机种类分为:硬件,操作系统,应用程序

生机勃勃. 文本操作基本流程

Computer连串分为:计算机硬件,操作系统,应用程序三片段。

咱俩用python或其余语言编写的应用程序若想要把数据永世保存下来,必必要保留于硬盘中,那就涉及到应用程序要操作硬件,名闻遐迩,应用程序是回天无力直接操作硬件的,那就用到了操作系统。操作系统把复杂的硬件操作封装成轻巧的接口给客商/应用程序使用,其粤语件正是操作系统提须要应用程序来操作硬盘虚构概念,客户或应用程序通过操作文件,可以将和谐的多少长久保存下去。

有了文件的定义,我们不需求再去思谋操作硬盘的内部意况,只要求关爱操作文件的流水生产线:

#1. 打开文件,得到文件句柄并赋值给一个变量
f=open('a.txt','r',encoding='utf-8') #默认打开模式就为r

#2. 通过句柄对文件进行操作
data=f.read()

#3. 关闭文件
f.close()

硬件:意在运营软件发生的通令。硬件包括CPU,内部存款和储蓄器,硬盘

关门文件的注意事项:

打开一个文件包含两部分资源:操作系统级打开的文件+应用程序的变量。在操作完毕一个文件时,必须把与该文件的这两部分资源一个不落地回收,回收方法为:
1、f.close() #回收操作系统级打开的文件
2、del f #回收应用程序级的变量

其中del f一定要发生在f.close()之后,否则就会导致操作系统打开的文件还没有关闭,白白占用资源,
而python自动的垃圾回收机制决定了我们无需考虑del f,这就要求我们,在操作完毕文件后,一定要记住f.close()

虽然我这么说,但是很多同学还是会很不要脸地忘记f.close(),对于这些不长脑子的同学,我们推荐傻瓜式操作方式:使用with关键字来帮我们管理上下文
with open('a.txt','w') as f:
    pass

with open('a.txt','r') as read_f,open('b.txt','w') as write_f:
    data=read_f.read()
    write_f.write(data)

注意

大大多CPU都有二种形式,即内核态与顾客态。
       

二. 文件编码

f=open(…)

是由操作系统张开文件,那么只要大家从不为open内定编码,那么张开文件的暗中同意编码很显然是操作系统说了算了

操作系统会用本身的暗中认可编码去开发布文书件,在windows下是gbk,在linux下是utf-8。

#这就用到了上节课讲的字符编码的知识:若要保证不乱码,文件以什么方式存的,就要以什么方式打开。
f=open('a.txt','r',encoding='utf-8')

①当cpu处于根本状态时,运维的是操作系统,能说了算硬件(能够博得具备cpu的指令集卡塔尔     

三. 文件的开采格局

文本句柄 = open(‘文件路线’,‘方式’卡塔尔

#1. 打开文件的模式有(默认为文本模式):
r ,只读模式【默认模式,文件必须存在,不存在则抛出异常】
w,只写模式【不可读;不存在则创建;存在则清空内容】
a, 只追加写模式【不可读;不存在则创建;存在则只追加内容】

#2. 对于非文本文件,我们只能使用b模式,"b"表示以字节的方式操作(而所有文件也都是以字节的形式存储的,使用这种模式无需考虑文本文件的字符编码、图片文件的jgp格式、视频文件的avi格式)
rb 
wb
ab
注:以b方式打开时,读取到的内容是字节类型,写入时也需要提供字节类型,不能指定编码

#3,‘+’模式(就是增加了一个功能)
r+, 读写【可读,可写】
w+,写读【可写,可读】
a+, 写读【可写,可读】

#4,以bytes类型操作的读写,写读,写读模式
r+b, 读写【可读,可写】
w+b,写读【可写,可读】
a+b, 写读【可写,可读】

②当cpu处于客户太状态时,运维的是顾客软件,不能说了算硬件(能够拿走具备cpu的通令集中的多少个子集,该子集不满含操作硬件的指令集卡塔尔国

四. 文件操作方法

图片 1 

4.1常用操作方法

read(3):

  1. 文书张开药格局为文本形式时,代表读取3个字符

  2. 文书展开药格局为b格局时,代表读取3个字节

此外的文本内光标移动都以以字节为单位的如:seek,tell,truncate

注意:

  1.
seek有三种运动格局0,1,2,此中1和2要求在b形式下进行,但不管哪一种方式,都以以bytes为单位活动的

  2.
truncate是截断文件,所以文件的张开药方式必需可写,可是不能用w或w+等形式展开,因为那样直接清空文件了,所以truncate要在r+或a或a+等形式下测试效果。

至于文件:

4.2有所操作方法

图片 2图片 3

class file(object)
    def close(self): # real signature unknown; restored from __doc__
        关闭文件
        """
        close() -> None or (perhaps) an integer.  Close the file.

        Sets data attribute .closed to True.  A closed file cannot be used for
        further I/O operations.  close() may be called more than once without
        error.  Some kinds of file objects (for example, opened by popen())
        may return an exit status upon closing.
        """

    def fileno(self): # real signature unknown; restored from __doc__
        文件描述符  
         """
        fileno() -> integer "file descriptor".

        This is needed for lower-level file interfaces, such os.read().
        """
        return 0    

    def flush(self): # real signature unknown; restored from __doc__
        刷新文件内部缓冲区
        """ flush() -> None.  Flush the internal I/O buffer. """
        pass


    def isatty(self): # real signature unknown; restored from __doc__
        判断文件是否是同意tty设备
        """ isatty() -> true or false.  True if the file is connected to a tty device. """
        return False


    def next(self): # real signature unknown; restored from __doc__
        获取下一行数据,不存在,则报错
        """ x.next() -> the next value, or raise StopIteration """
        pass

    def read(self, size=None): # real signature unknown; restored from __doc__
        读取指定字节数据
        """
        read([size]) -> read at most size bytes, returned as a string.

        If the size argument is negative or omitted, read until EOF is reached.
        Notice that when in non-blocking mode, less data than what was requested
        may be returned, even if no size parameter was given.
        """
        pass

    def readinto(self): # real signature unknown; restored from __doc__
        读取到缓冲区,不要用,将被遗弃
        """ readinto() -> Undocumented.  Don't use this; it may go away. """
        pass

    def readline(self, size=None): # real signature unknown; restored from __doc__
        仅读取一行数据
        """
        readline([size]) -> next line from the file, as a string.

        Retain newline.  A non-negative size argument limits the maximum
        number of bytes to return (an incomplete line may be returned then).
        Return an empty string at EOF.
        """
        pass

    def readlines(self, size=None): # real signature unknown; restored from __doc__
        读取所有数据,并根据换行保存值列表
        """
        readlines([size]) -> list of strings, each a line from the file.

        Call readline() repeatedly and return a list of the lines so read.
        The optional size argument, if given, is an approximate bound on the
        total number of bytes in the lines returned.
        """
        return []

    def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
        指定文件中指针位置
        """
        seek(offset[, whence]) -> None.  Move to new file position.

        Argument offset is a byte count.  Optional argument whence defaults to
(offset from start of file, offset should be >= 0); other values are 1
        (move relative to current position, positive or negative), and 2 (move
        relative to end of file, usually negative, although many platforms allow
        seeking beyond the end of a file).  If the file is opened in text mode,
        only offsets returned by tell() are legal.  Use of other offsets causes
        undefined behavior.
        Note that not all file objects are seekable.
        """
        pass

    def tell(self): # real signature unknown; restored from __doc__
        获取当前指针位置
        """ tell() -> current file position, an integer (may be a long integer). """
        pass

    def truncate(self, size=None): # real signature unknown; restored from __doc__
        截断数据,仅保留指定之前数据
        """
        truncate([size]) -> None.  Truncate the file to at most size bytes.

        Size defaults to the current file position, as returned by tell().
        """
        pass

    def write(self, p_str): # real signature unknown; restored from __doc__
        写内容
        """
        write(str) -> None.  Write string str to file.

        Note that due to buffering, flush() or close() may be needed before
        the file on disk reflects the data written.
        """
        pass

    def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
        将一个字符串列表写入文件
        """
        writelines(sequence_of_strings) -> None.  Write the strings to the file.

        Note that newlines are not added.  The sequence can be any iterable object
        producing strings. This is equivalent to calling write() for each string.
        """
        pass

    def xreadlines(self): # real signature unknown; restored from __doc__
        可用于逐行读取文件,非全部
        """
        xreadlines() -> returns self.

        For backward compatibility. File objects now include the performance
        optimizations previously implemented in the xreadlines module.
        """
        pass

2.x

图片 4图片 5

class TextIOWrapper(_TextIOBase):
    """
    Character and line based layer over a BufferedIOBase object, buffer.

    encoding gives the name of the encoding that the stream will be
    decoded or encoded with. It defaults to locale.getpreferredencoding(False).

    errors determines the strictness of encoding and decoding (see
    help(codecs.Codec) or the documentation for codecs.register) and
    defaults to "strict".

    newline controls how line endings are handled. It can be None, '',
    'n', 'r', and 'rn'.  It works as follows:

    * On input, if newline is None, universal newlines mode is
      enabled. Lines in the input can end in 'n', 'r', or 'rn', and
      these are translated into 'n' before being returned to the
      caller. If it is '', universal newline mode is enabled, but line
      endings are returned to the caller untranslated. If it has any of
      the other legal values, input lines are only terminated by the given
      string, and the line ending is returned to the caller untranslated.

    * On output, if newline is None, any 'n' characters written are
      translated to the system default line separator, os.linesep. If
      newline is '' or 'n', no translation takes place. If newline is any
      of the other legal values, any 'n' characters written are translated
      to the given string.

    If line_buffering is True, a call to flush is implied when a call to
    write contains a newline character.
    """
    def close(self, *args, **kwargs): # real signature unknown
        关闭文件
        pass

    def fileno(self, *args, **kwargs): # real signature unknown
        文件描述符  
        pass

    def flush(self, *args, **kwargs): # real signature unknown
        刷新文件内部缓冲区
        pass

    def isatty(self, *args, **kwargs): # real signature unknown
        判断文件是否是同意tty设备
        pass

    def read(self, *args, **kwargs): # real signature unknown
        读取指定字节数据
        pass

    def readable(self, *args, **kwargs): # real signature unknown
        是否可读
        pass

    def readline(self, *args, **kwargs): # real signature unknown
        仅读取一行数据
        pass

    def seek(self, *args, **kwargs): # real signature unknown
        指定文件中指针位置
        pass

    def seekable(self, *args, **kwargs): # real signature unknown
        指针是否可操作
        pass

    def tell(self, *args, **kwargs): # real signature unknown
        获取指针位置
        pass

    def truncate(self, *args, **kwargs): # real signature unknown
        截断数据,仅保留指定之前数据
        pass

    def writable(self, *args, **kwargs): # real signature unknown
        是否可写
        pass

    def write(self, *args, **kwargs): # real signature unknown
        写内容
        pass

    def __getstate__(self, *args, **kwargs): # real signature unknown
        pass

    def __init__(self, *args, **kwargs): # real signature unknown
        pass

    @staticmethod # known case of __new__
    def __new__(*args, **kwargs): # real signature unknown
        """ Create and return a new object.  See help(type) for accurate signature. """
        pass

    def __next__(self, *args, **kwargs): # real signature unknown
        """ Implement next(self). """
        pass

    def __repr__(self, *args, **kwargs): # real signature unknown
        """ Return repr(self). """
        pass

    buffer = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    closed = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    encoding = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    errors = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    line_buffering = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    name = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    newlines = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    _CHUNK_SIZE = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

    _finalizing = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

3.x

3.x

  • 文件能够积存分化品种的音讯,叁个文书能够富含文本,图片,录制,Computer程序等剧情。
  • 微处理器上硬盘上具有的剧情都以以文件的样式储存。程序便是由一个要么七个公文构成的。
  • 文本对象是python代码对Computer上海外国语大学部文件的要害接口。

五. 文件的改动

文件的数码是存放在于硬盘上的,因此只存在覆盖、荒诞不经更改这么一说,我们一直见到的改变文件,都以模仿出来的成效,具体的说有二种达成格局:

措施后生可畏:将硬盘存放的该文件的剧情全方位加载到内部存款和储蓄器,在内部存款和储蓄器中是足以改良的,更改达成后,再由内部存款和储蓄器覆盖到硬盘(word,vim,nodpad++等编辑器卡塔 尔(阿拉伯语:قطر‎

图片 6图片 7

import os  # 调用系统模块

with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:
    data=read_f.read() #全部读入内存,如果文件很大,会很卡
    data=data.replace('alex','SB') #在内存中完成修改

    write_f.write(data) #一次性写入新文件

os.remove('a.txt')  #删除原文件
os.rename('.a.txt.swap','a.txt')   #将新建的文件重命名为原文件

方法一

方式二:将硬盘存放的该文件的内容后生可畏行黄金年代行地读入内部存款和储蓄器,校订完成就写入新文件,最终用新文件覆盖源文件

图片 8图片 9

import os

with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:
    for line in read_f:
        line=line.replace('alex','SB')
        write_f.write(line)

os.remove('a.txt')
os.rename('.a.txt.swap','a.txt') 

方法二

文件属性:

六. 当日练习

  1. 文本a.txt内容:每风姿罗曼蒂克行内容分别为商品名字,价钱,个数。

apple 10 3

tesla 100000 1

mac 3000 2

lenovo 30000 3

chicken 10 3

经过代码,将其营造设成这种数据类型:[{‘name’:’apple’,’price’:10,’amount’:3},{‘name’:’tesla’,’price’:1000000,’amount’:1}……]
并思忖出总价值钱。

2,犹如下文件:


alex是老男孩python发起人,创造人。

alex其实是人妖。

谁说alex是sb?

你们真逗,alex再牛逼,也掩盖不住资深土冒的派头。


将文件中存有的alex都替换到大写的SB。

  名字

  类型(注解文件数据类型,是图表,音乐,还是文本卡塔 尔(阿拉伯语:قطر‎

  位置(存款和储蓄在哪儿卡塔 尔(英语:State of Qatar)

  大小(文件中有个别许字节卡塔 尔(英语:State of Qatar)

文件名:

  大部分操作系统中(包括Windows卡塔 尔(英语:State of Qatar),文件名中有生机勃勃部分用来提示文件中蕴藏怎么样品种的数量。文件名中不可胜道最少有多少个点(.卡塔 尔(阿拉伯语:قطر‎,点前面的生龙活虎部分提出了文本的种类。那大器晚成部分称作扩展名(extension)

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