File Objects

.. highlightlang:: c

.. _fileobjects:

.. 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.