File Objects
************

These APIs are a minimal emulation of the Python 2 C API for built-in
file objects, which used to rely on the buffered I/O ("FILE*") support
from the C standard library.  In Python 3, files and streams use the
new "io" module, which defines several layers over the low-level
unbuffered I/O of the operating system.  The functions described below
are convenience C wrappers over these new APIs, and meant mostly for
internal error reporting in the interpreter; third-party code is
advised to access the "io" APIs instead.

PyFile_FromFd(int fd, const char *name, const char *mode, int buffering, const char *encoding, const char *errors, const char *newline, int closefd)

   Create a Python file object from the file descriptor of an already
   opened file *fd*.  The arguments *name*, *encoding*, *errors* and
   *newline* can be *NULL* to use the defaults; *buffering* can be
   *-1* to use the default. *name* is ignored and kept for backward
   compatibility. Return *NULL* on failure. For a more comprehensive
   description of the arguments, please refer to the "io.open()"
   function documentation.

   警告: Since Python streams have their own buffering layer, mixing
     them with OS-level file descriptors can produce various issues
     (such as unexpected ordering of data).

   在 3.2 版更改: Ignore *name* attribute.

int PyObject_AsFileDescriptor(PyObject *p)

   Return the file descriptor associated with *p* as an "int".  If the
   object is an integer, its value is returned.  If not, the object's
   "fileno()" method is called if it exists; the method must return an
   integer, which is returned as the file descriptor value.  Sets an
   exception and returns "-1" on failure.

PyObject* PyFile_GetLine(PyObject *p, int n)
    *Return value: New reference.*

   Equivalent to "p.readline([n])", this function reads one line from
   the object *p*.  *p* may be a file object or any object with a
   "readline()" method.  If *n* is "0", exactly one line is read,
   regardless of the length of the line.  If *n* is greater than "0",
   no more than *n* bytes will be read from the file; a partial line
   can be returned.  In both cases, an empty string is returned if the
   end of the file is reached immediately.  If *n* is less than "0",
   however, one line is read regardless of length, but "EOFError" is
   raised if the end of the file is reached immediately.

int PyFile_WriteObject(PyObject *obj, PyObject *p, int flags)

   Write object *obj* to file object *p*.  The only supported flag for
   *flags* is "Py_PRINT_RAW"; if given, the "str()" of the object is
   written instead of the "repr()".  Return "0" on success or "-1" on
   failure; the appropriate exception will be set.

int PyFile_WriteString(const char *s, PyObject *p)

   Write string *s* to file object *p*.  Return "0" on success or "-1"
   on failure; the appropriate exception will be set.
