python中的open()函數

open函數，該函數用於文件處理

操作文件時，一般需要經歷如下步驟：

• 打開文件
• 操作文件

一、打開文件

1	文件句柄  =  open ( '文件路徑' ,  '模式' )

打開文件時，需要指定文件路徑和以何等方式打開文件，打開后，即可獲取該文件句柄，日后通過此文件句柄對該文件操作。

打開文件的模式有：

• r ，只讀模式【默認】
• w，只寫模式【不可讀；不存在則創建；存在則清空內容；】
• x， 只寫模式【不可讀；不存在則創建，存在則報錯】
• a， 追加模式【可讀；   不存在則創建；存在則只追加內容；】

"+" 表示可以同時讀寫某個文件

• r+， 讀寫【可讀，可寫】
• w+，寫讀【可讀，可寫】
• x+ ，寫讀【可讀，可寫】
• a+， 寫讀【可讀，可寫】

 "b"表示以字節的方式操作

• rb  或 r+b
• wb 或 w+b
• xb 或 w+b
• ab 或 a+b

 注：以b方式打開時，讀取到的內容是字節類型，寫入時也需要提供字節類型

 

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 '\r\n'.  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 '\r\n', 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
        關閉文件
        pass

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

    def flush(self, *args, **kwargs): # real signature unknown
        刷新文件內部緩沖區
        pass

    def isatty(self, *args, **kwargs): # real signature unknown
        判斷文件是否是同意tty設備
        pass

    def read(self, *args, **kwargs): # real signature unknown
        讀取指定字節數據
        pass

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

    def readline(self, *args, **kwargs): # real signature unknown
        僅讀取一行數據
        pass

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

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

    def tell(self, *args, **kwargs): # real signature unknown
        獲取指針位置
        pass

    def truncate(self, *args, **kwargs): # real signature unknown
        截斷數據，僅保留指定之前數據
        pass

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

    def write(self, *args, **kwargs): # real signature unknown
        寫內容
        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

三、管理上下文

為了避免打開文件后忘記關閉，可以通過管理上下文，即：

1 2 3

with  open ( 'log' , 'r' ) as f:               ...

如此方式，當with代碼塊執行完畢時，內部會自動關閉並釋放文件資源。

在Python 2.7 及以后，with又支持同時對多個文件的上下文進行管理，即：

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

 例：