文件操作以及序列化,python之文件操作

Computer连串分为:硬件,操作系统,应用程序

大器晚成. 文件操作基本流程

Computer系列分为:Computer硬件,操作系统,应用程序三局地。

大家用python或任何语言编写的应用程序若想要把数量恒久保存下去,一定要封存于硬盘中,那就事关到应用程序要操作硬件,人所共知,应用程序是无可奈何直接操作硬件的,那就用到了操作系统。操作系统把纷纭的硬件操作封装成简单的接口给客户/应用程序使用,其汉语件正是操作系统提需要应用程序来操作硬盘虚构概念,顾客或应用程序通过操作文件,能够将团结的数量恒久保存下去。

有了文本的概念,大家不须求再去思考操作硬盘的内部原因,只须求关爱操作文件的流程:

#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:意在运转软件产生的授命。硬件包蕴CPU,内存,硬盘

关闭文件的注意事项:

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

绝大多数CPU都有两种情势,即内核态与客商态。
       

二. 文件编码

f=open(…)

是由操作系统张开文件,那么只要大家从未为open指确定人员编制码,那么张开文件的暗中同意编码很鲜明是操作系统说了算了

操作系统会用自个儿的暗中同意编码去开拓文件,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,运转的是操作系统,能调整硬件(可以收获具备cpu的指令集)     

三. 文件的展开情势

文本句柄 = open(‘文件路线’,‘情势’)

#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,运营的是客户软件,不可能调整硬件(能够拿到具备cpu的授命聚焦的一个子集,该子集不包涵操作硬件的指令集)

四. 文件操作方法

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4.1常用操作方法

read(3):

  1. 文件展开情势为文本方式时,代表读取3个字符

  2. 文件打开药方式为b情势时,代表读取3个字节

别的的文件内光标移动都以以字节为单位的如:seek,tell,truncate

注意:

  1.
seek有二种运动格局0,1,2,此中1和2不得不在b情势下开展,但无论是哪一类情势,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得可写,不过不能够用w或w+等方法张开,因为那样直接清空文件了,所以truncate要在r+或a或a+等情势下测量检验效果。

有关文件:

4.2享有操作方法

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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

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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

  • 文件能够积存分裂等级次序的音信,一个文件能够分包文本,图片,摄像,Computer程序等剧情。
  • Computer上硬盘上有所的始末都是以文件的方式储存。程序就是由二个依旧七个文本构成的。
  • 文本对象是python代码对Computer上国外国语高校部文件的关键接口。

五. 文件的退换

文件的数码是寄存在于硬盘上的,因此只设有覆盖、子虚乌有改革这么一说,大家一贯看来的退换文件,都以模仿出来的效果与利益,具体的说有二种完结方式:

格局生龙活虎:将硬盘寄存的该文件的内容总体加载到内存,在内部存款和储蓄器中是足以改过的,匡正完成后,再由内部存款和储蓄器覆盖到硬盘(word,vim,nodpad++等编辑器)

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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

办法二:将硬盘贮存的该公文的源委意气风发行业作风度翩翩行地读入内部存款和储蓄器,纠正完结就写入新文件,最终用新文件覆盖源文件

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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. 文件a.txt内容:每豆蔻梢头行内容分别为物品名字,价钱,个数。

apple 10 3

tesla 100000 1

mac 3000 2

lenovo 30000 3

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透过代码,将其构建设成这种数据类型:[{‘name’:’apple’,’price’:10,’amount’:3},{‘name’:’tesla’,’price’:1000000,’amount’:1}……]
并思量出总的价值钱。

2,宛如下文件:


alex是老男孩python发起人,创立人。

alex其实是人妖。

谁说alex是sb?

你们真逗,alex再牛逼,也蒙蔽不住资深土憋的风采。


将文件中负有的alex都替换到大写的SB。

  名字

  类型(评释文件数据类型,是图形,音乐,依旧文本)

  地方(存储在何地)

  大小(文件中有个别许字节)

文件名:

  繁多操作系统中(包罗Windows),文件名中有局地用来提示文件中满含怎么着品种的数量。文件名中见怪不怪最稀少二个点(.),点后边的意气风发对提出了文件的连串。那风流罗曼蒂克部分堪当扩展名(extension)

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