python中的open函数

open函数用于文件处理

操作文件时，一般需要经历如下步骤：

• 打开文件
• 操作文件

一、打开文件

1	文件句柄 = open('文件路径', '模式')

打开文件时，需要指定文件路径和以何等方式打开文件，打开后，即可获取该文件句柄，日后通过此文件句柄对该文件操作。

打开文件的模式有：

• r ，只读模式【默认】
• w，只写模式【不可读；不存在则创建；存在则清空内容；】
• x， 只写模式【不可读；不存在则创建，存在则报错】
• a， 追加模式【不可读； 不存在则创建；存在则只追加内容；】

"+" 表示可以同时读写某个文件

• r+， 读写【可读，可写】
• w+，写读【可读，可写】
• x+ ，写读【可读，可写】
• a+， 写读【可读，可写】

"b"表示以字节的方式操作

• 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

二、操作

 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

2.x

 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
         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

三、管理上下文

为了避免打开文件后忘记关闭，可以通过管理上下文，即：

1 2 3

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

如此方式，当with代码块执行完毕时，内部会自动关闭并释放文件资源。

在Python 2.7 及以后，with又支持同时对多个文件的上下文进行管理，即：

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