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.. highlightlang:: c
.. _fileobjects:
File Objects
------------
.. index:: object: file
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 (:c:type:`FILE\*`) support
from the C standard library. In Python 3, files and streams use the new
:mod:`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 :mod:`io` APIs instead.
.. c:function:: PyFile_FromFd(int fd, char *name, char *mode, int buffering, char *encoding, char *errors, 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 :func:`io.open` function documentation.
.. warning::
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).
.. versionchanged:: 3.2
Ignore *name* attribute.
.. c:function:: int PyObject_AsFileDescriptor(PyObject *p)
Return the file descriptor associated with *p* as an :c:type:`int`. If the
object is an integer, its value is returned. If not, the
object's :meth:`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.
.. c:function:: PyObject* PyFile_GetLine(PyObject *p, int n)
.. index:: single: EOFError (built-in exception)
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 :meth:`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 :exc:`EOFError` is
raised if the end of the file is reached immediately.
.. c:function:: int PyFile_WriteObject(PyObject *obj, PyObject *p, int flags)
.. index:: single: Py_PRINT_RAW
Write object *obj* to file object *p*. The only supported flag for *flags* is
:const:`Py_PRINT_RAW`; if given, the :func:`str` of the object is written
instead of the :func:`repr`. Return ``0`` on success or ``-1`` on failure; the
appropriate exception will be set.
.. c:function:: 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.
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