File Objects

.. highlight:: c

.. _fileobjects:

.. index:: pair: 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:expr: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:: PyObject* 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:expr: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_SetOpenCodeHook(Py_OpenCodeHookFunction handler)

Overrides the normal behavior of :func:io.open_code to pass its parameter through the provided handler.

The handler is a function of type:

.. c:namespace:: NULL .. c:type:: PyObject * (*Py_OpenCodeHookFunction)(PyObject *, void *)

  Equivalent of :c:expr:`PyObject *(\*)(PyObject *path,
  void *userData)`, where *path* is guaranteed to be
  :c:type:`PyUnicodeObject`.

The userData pointer is passed into the hook function. Since hook functions may be called from different runtimes, this pointer should not refer directly to Python state.

As this hook is intentionally used during import, avoid importing new modules during its execution unless they are known to be frozen or available in sys.modules.

Once a hook has been set, it cannot be removed or replaced, and later calls to :c:func:PyFile_SetOpenCodeHook will fail. On failure, the function returns -1 and sets an exception if the interpreter has been initialized.

This function is safe to call before :c:func:Py_Initialize.

.. audit-event:: setopencodehook "" c.PyFile_SetOpenCodeHook

.. versionadded:: 3.8

.. c:function:: PyObject *PyFile_OpenCodeObject(PyObject *path)

Open path with the mode 'rb'. path must be a Python :class:str object. The behavior of this function may be overridden by :c:func:PyFile_SetOpenCodeHook to allow for some preprocessing of the text.

This is analogous to :func:io.open_code in Python.

On success, this function returns a :term:strong reference to a Python file object. On failure, this function returns NULL with an exception set.

.. versionadded:: 3.8

.. c:function:: PyObject *PyFile_OpenCode(const char *path)

Similar to :c:func:PyFile_OpenCodeObject, but path is a UTF-8 encoded :c:expr:const char*.

.. versionadded:: 3.8

.. c:function:: int PyFile_WriteObject(PyObject *obj, PyObject *p, int flags)

.. index:: single: Py_PRINT_RAW (C macro)

Write object obj to file object p. The only supported flag for flags is :c:macro:Py_PRINT_RAW; if given, the :func:str of the object is written instead of the :func:repr.

If obj is NULL, write the string "<NULL>".

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.

Deprecated API ^^^^^^^^^^^^^^

These are :term:soft deprecated APIs that were included in Python's C API by mistake. They are documented solely for completeness; use other PyFile* APIs instead.

.. c:function:: PyObject *PyFile_NewStdPrinter(int fd)

Use :c:func:PyFile_FromFd with defaults (fd, NULL, "w", -1, NULL, NULL, NULL, 0) instead.

.. c:var:: PyTypeObject PyStdPrinter_Type

Type of file-like objects used internally at Python startup when :py:mod:io is not yet available. Use Python :py:func:open or :c:func:PyFile_FromFd to create file objects instead.