os.name

The name of the operating system dependent module imported.
Windows 返回 nt; Linux 返回posix

os.open() v.s. open() v.s. io.open()

• file descriptor v.s. file object
  下图摘自: zhangfan_lovebk 同学 文件描述符（fd）与file结构体及其关系

os

下图摘自 fasionchan 同学 的 Linux文件描述符

fd.png

总之呢，file descriptor 只是 一个非负整数，用作文件描述符表的索引；

file object：An object exposing a file-oriented API (with methods such as read() or write()) to an underlying resource.File objects are also called file-like objects or streams.There are actually three categories of file objects: raw binary files, buffered binary files and text files.

• os.open(path, flags, mode=0o777, *, dir_fd=None)
  Return the file descriptor for the newly opened file.

• io.open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)
  This is an alias for the builtin open() function.

• open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)
  Open file and return a corresponding file object.

• class io.IOBase

  • fileno()
    Return the underlying file descriptor (an integer) of the stream if it exists.

• os.fdopen(fd, *args, **kwargs)
  Return an open file object connected to the file descriptor fd.

在 Lib/os.py 中的定义：

def fdopen(fd, *args, **kwargs):
    if not isinstance(fd, int):
        raise TypeError("invalid fd type (%s, expected integer)" % type(fd))
    import io
    return io.open(fd, *args, **kwargs)

Tornado v1.0.0 源码

• ioloop.py

  self._waker_reader = os.fdopen(r, "r", 0)
  self._waker_writer = os.fdopen(w, "w", 0)

由上面可知，os.fdopen()调用的是 io.open(), 故会调用 open(file, mode='r', buffering=-1, ...)
其中,

• mode: mode is an optional string that specifies the mode in which the file is opened. It defaults to 'r' which means open for reading in text mode.

  • r: open for reading (default)
    w: open for writing, truncating the file first
    x: open for exclusive creation, failing if the file already exists
    a: open for writing, appending to the end of the file if it exists
    b: binary mode
    t: text mode (default)
    +: open a disk file for updating (reading and writing)
    U: universal newlines mode (deprecated)

• buffering: buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size in bytes of a fixed-size chunk buffer. When no buffering argument is given, 则默认分配。