• DAY 8 文件管理


    文件管理 

         r ,只读模式【默认模式,文件必须存在,不存在则抛出异常】
    
           rb
    
         w,只写模式【不可读;不存在则创建;存在则清空内容】
    
           wb
    
         a, 只追加写模式【不可读;不存在则创建;存在则只追加内容】
            重点(a模式下:
                1.如果是write()
                 2.seek() 光标移动(修改)无效           )        ab

    读写    

         r+        同下
    
           r+b
    
         w+      #永远都是在最后写,当然也可以用seek(光标)来定位
    
           w+b
    
         a+        永远只能在最后写
    
           a+b


    '+'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】


    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】

    注:带b的永远都是字节类型

    文件指针

    seek的参数永远都是字节
    tell读取当前指针的位置
    int = input()
    f.seek(f.tell)从当前位置开始向后覆盖的内容
    obj.flush()    #强刷将内容强行写入硬盘
    涉及内容:断点续传


    文件的截取:
      obj.seek()
      obj.truncate()  #截取 根据指针来截取

     文件的读取

    for  line  in   obj:
    
      print(line)
    
    循环打印每一行的内容
    
    目的:节省内存,读完即删(python垃圾回收机制)

    操作文件三要素

      

    1.路径:
    
      2.编码:utf-8
    
      3.模式:只读 r,只写,读写……

    模式

      ·1.只读

      分为两种:

        ·1.只读:

        

    ——open(文件路径,mode = 'rb')  #这一种必需把010101转化成bytes类型
    
    ——open(文件路径,mode = 'r',encoding = 'utf-8')

        `2.只写:

        

    ——open(文件路径,mode = 'w')    #这一种必需把010101转化成bytes类型
    
    ——open(文件路径,encoding = ‘utf-8’,mode = 'wb')

     

         3.只追加

        

    ——open(文件路径,mode = 'ab')     #这一种必需把010101转化成bytes类型
    
    ——open(文件路径,mode = 'a',encoding = 'utf-8')

     

    obj.read()
    obj.write()
    obj.seek()
    obj.tell()
    obj.close()
    obj.flush()
    obj.readline()
    obj.readlines()    #打印一个列表
    python2 :obj.xreadlines() = python3里的for循环
    python2 全部方法:
    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
    
    

    python3全部方法:

    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, '',
        '
    ', '
    ', and '
    '.  It works as follows:
        
        * On input, if newline is None, universal newlines mode is
          enabled. Lines in the input can end in '
    ', '
    ', or '
    ', and
          these are translated into '
    ' 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 '
    ' characters written are
          translated to the system default line separator, os.linesep. If
          newline is '' or '
    ', no translation takes place. If newline is any
          of the other legal values, any '
    ' 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
     

    文件的打开与关闭方式

    手动关闭: obj.close()
    自动关闭:with open(文件路径,mode = 'rb')as obj:
        obj.read()
        代码执行完毕后:自动关闭



    光标:

    read(3)

    1. 文件打开方式为文本模式时,代表读取3个字符
    
      2. 文件打开方式为b模式时,代表读取3个字节
    
    其余的文件内光标移动都是以字节为单位的如:seek,tell,truncate
    
    注意:
    
      1. seek有三种移动方式0,1,2,其中1和2必须在b模式下进行,但无论哪种模式,都是以bytes为单位移动的
    
      2. truncate是截断文件,所以文件的打开方式必须可写,但是不能用w或w+等方式打开,因为那样直接清空文件了,所以truncate要在r+或a或a+等模式下测试效果。

     

    注意事项

     读和写不可以同时进行
    
      r/r+打开文件的时候,不会清空文件
    
      当用户读取操作之后,写的所有内容都变成缩写
    
      当用户不执行读操作,写默认从开始覆盖
    
      不要同时读写一个操作文件
    复制代码

    五,文件的修改。

    文件的数据是存放于硬盘上的,因而只存在覆盖、不存在修改这么一说,我们平时看到的修改文件,都是模拟出来的效果,具体的说有两种实现方式:

    方式一:将硬盘存放的该文件的内容全部加载到内存,在内存中是可以修改的,修改完毕后,再由内存覆盖到硬盘(word,vim,nodpad++等编辑器)

    复制代码
    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
    复制代码

    方式二:将硬盘存放的该文件的内容一行一行地读入内存,修改完毕就写入新文件,最后用新文件覆盖源文件

    复制代码
    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') 
    复制代码
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  • 原文地址:https://www.cnblogs.com/zsdbk/p/8659185.html
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