cpython/Doc/c-api/file.rst

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.. highlightlang:: c
.. _fileobjects:
File Objects
------------
.. index:: object: file
Python's built-in file objects are implemented entirely on the :ctype:`FILE\*`
support from the C standard library. This is an implementation detail and may
change in future releases of Python. The ``PyFile_`` APIs are a wrapper over
the :mod:`io` module.
.. cfunction:: PyFile_FromFd(int fd, char *name, char *mode, int buffering, char *encoding, char *newline, int closefd)
Create a new :ctype:`PyFileObject` from the file descriptor of an already
opened file *fd*. The arguments *name*, *encoding* and *newline* can be
*NULL* to use the defaults; *buffering* can be *-1* to use the default.
Return *NULL* on failure.
.. warning::
Take care when you are mixing streams and descriptors! For more
information, see `the GNU C Library docs
<http://www.gnu.org/software/libc/manual/html_node/Stream_002fDescriptor-Precautions.html#Stream_002fDescriptor-Precautions>`_.
.. cfunction:: int PyObject_AsFileDescriptor(PyObject *p)
Return the file descriptor associated with *p* as an :ctype:`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.
.. cfunction:: 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.
.. cfunction:: 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.
.. cfunction:: 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.