File Objects — Python 3.6.5 documentation

# File Objects

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 (`FILE*`) support from the C standard library. In Python 3, files and streams use the new `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 `io` APIs instead.

`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 `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).

  Changed in version 3.2: Ignore name attribute.

int `PyObject_AsFileDescriptor`(PyObject *p)

  Return the file descriptor associated with p as an `int`. If the object is an integer, its value is returned. If not, the object’s `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.

PyObject* `PyFile_GetLine`(PyObject *p, int n)
  Return value: New reference.

  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 `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 `EOFError` is raised if the end of the file is reached immediately.

int `PyFile_WriteObject`(PyObject *obj, PyObject *p, int flags)

  Write object obj to file object p. The only supported flag for flags is `Py_PRINT_RAW`; if given, the `str()` of the object is written instead of the `repr()`. Return `0` on success or `-1` on failure; the appropriate exception will be set.

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.