Python 3.6.5 Documentation >  File Objects

File Objects
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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.