.. highlightlang:: c

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, 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 :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:`~io.IOBase.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:`~io.IOBase.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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