Patch 1329 (partial) by Christian Heimes.

Add a closefd flag to open() which can be set to False to prevent closing
the file descriptor when close() is called or when the object is destroyed.
Useful to ensure that sys.std{in,out,err} keep their file descriptors open
when Python is uninitialized.  (This was always a feature in 2.x, it just
wasn't implemented in 3.0 yet.)

Doc/c-api/concrete.rst

@@ -2401,12 +2401,12 @@ change in future releases of Python.
    :ctype:`PyFileObject`.
 
 
-.. cfunction:: PyFile_FromFd(int fd, char *name, char *mode, int buffering, char *encoding, char *newline)
+.. 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* as well as buffering can be *-1* to use the defaults. Return *NULL* on
-   failure.
+   *NULL* to use the defaults; *buffering* can be *-1* to use the default.
+   Return *NULL* on failure.
 
    .. warning::
 

Include/fileobject.h

@@ -8,7 +8,8 @@ extern "C" {
 
 #define PY_STDIOTEXTMODE "b"
 
-PyAPI_FUNC(PyObject *) PyFile_FromFd(int, char *, char *, int, char *, char *);
+PyAPI_FUNC(PyObject *) PyFile_FromFd(int, char *, char *, int, char *, char *,
+				     int);
 PyAPI_FUNC(PyObject *) PyFile_GetLine(PyObject *, int);
 PyAPI_FUNC(int) PyFile_WriteObject(PyObject *, PyObject *, int);
 PyAPI_FUNC(int) PyFile_WriteString(const char *, PyObject *);

Lib/io.py

@@ -49,7 +49,8 @@ class BlockingIOError(IOError):
         self.characters_written = characters_written
 
 
-def open(file, mode="r", buffering=None, encoding=None, newline=None):
+def open(file, mode="r", buffering=None, encoding=None, newline=None,
+         closefd=True):
     r"""Replacement for the built-in open function.
 
     Args:
@@ -81,9 +82,12 @@ def open(file, mode="r", buffering=None, encoding=None, newline=None):
           other legal values, any `'\n'` characters written are
           translated to the given string.
 
+      closefd: optional argument to keep the underlying file descriptor
+               open when the file is closed.  It must not be false when
+               a filename is given.
+
     (*) If a file descriptor is given, it is closed when the returned
-    I/O object is closed.  If you don't want this to happen, use
-    os.dup() to create a duplicate file descriptor.
+    I/O object is closed, unless closefd=False is give.
 
     Mode strings characters:
       'r': open for reading (default)
@@ -138,7 +142,8 @@ def open(file, mode="r", buffering=None, encoding=None, newline=None):
                  (reading and "r" or "") +
                  (writing and "w" or "") +
                  (appending and "a" or "") +
-                 (updating and "+" or ""))
+                 (updating and "+" or ""),
+                 closefd)
     if buffering is None:
         buffering = -1
     if buffering < 0 and raw.isatty():

Lib/quopri.py

@@ -227,12 +227,14 @@ def main():
                 sys.stderr.write("%s: can't open (%s)\n" % (file, msg))
                 sts = 1
                 continue
-        if deco:
-            decode(fp, sys.stdout.buffer)
-        else:
-            encode(fp, sys.stdout.buffer, tabs)
-        if fp is not sys.stdin:
-            fp.close()
+        try:
+            if deco:
+                decode(fp, sys.stdout.buffer)
+            else:
+                encode(fp, sys.stdout.buffer, tabs)
+        finally:
+            if file != '-':
+                fp.close()
     if sts:
         sys.exit(sts)
 

Lib/test/test_io.py

@@ -259,6 +259,9 @@ class IOTest(unittest.TestCase):
         self.assertEqual(f.write(a), n)
         f.close()
 
+    def test_closefd(self):
+        self.assertRaises(ValueError, io.open, test_support.TESTFN, 'w',
+                          closefd=False)
 
 class MemorySeekTestMixin:
 

Misc/NEWS

@@ -28,6 +28,9 @@ Core and Builtins
   with `Py_FileSystemDefaultEncoding` and a new API method 
   `PyUnicode_DecodeFSDefault(char*)` was added.
 
+- io.open() and _fileio.FileIO have grown a new argument closefd. A false
+  value disables the closing of the file descriptor.
+
 Extension Modules
 -----------------
 

Modules/_fileio.c

@@ -33,6 +33,7 @@ typedef struct {
 	unsigned readable : 1;
 	unsigned writable : 1;
 	int seekable : 2; /* -1 means unknown */
+	int closefd : 1;
 	PyObject *weakreflist;
 } PyFileIOObject;
 
@@ -59,6 +60,13 @@ internal_close(PyFileIOObject *self)
 static PyObject *
 fileio_close(PyFileIOObject *self)
 {
+	if (!self->closefd) {
+		if (PyErr_WarnEx(PyExc_RuntimeWarning,
+				 "Trying to close unclosable fd!", 3) < 0) {
+			return NULL;
+		}
+		Py_RETURN_NONE;
+	}
 	errno = internal_close(self);
 	if (errno < 0) {
 		PyErr_SetFromErrno(PyExc_IOError);
@@ -119,7 +127,7 @@ static int
 fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 {
 	PyFileIOObject *self = (PyFileIOObject *) oself;
-	static char *kwlist[] = {"file", "mode", NULL};
+	static char *kwlist[] = {"file", "mode", "closefd", NULL};
 	char *name = NULL;
 	char *mode = "r";
 	char *s;
@@ -130,6 +138,7 @@ fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 	int rwa = 0, plus = 0, append = 0;
 	int flags = 0;
 	int fd = -1;
+	int closefd = 1;
 
 	assert(PyFileIO_Check(oself));
 	if (self->fd >= 0) {
@@ -138,8 +147,8 @@ fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 			return -1;
 	}
 
-	if (PyArg_ParseTupleAndKeywords(args, kwds, "i|s:fileio",
-					kwlist, &fd, &mode)) {
+	if (PyArg_ParseTupleAndKeywords(args, kwds, "i|si:fileio",
+					kwlist, &fd, &mode, &closefd)) {
 		if (fd < 0) {
 			PyErr_SetString(PyExc_ValueError,
 					"Negative filedescriptor");
@@ -153,8 +162,9 @@ fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 	    if (GetVersion() < 0x80000000) {
 		/* On NT, so wide API available */
 		PyObject *po;
-		if (PyArg_ParseTupleAndKeywords(args, kwds, "U|s:fileio",
-						kwlist, &po, &mode)) {
+		if (PyArg_ParseTupleAndKeywords(args, kwds, "U|si:fileio",
+						kwlist, &po, &mode, &closefd)
+						) {
 			widename = PyUnicode_AS_UNICODE(po);
 		} else {
 			/* Drop the argument parsing error as narrow
@@ -162,13 +172,13 @@ fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 			PyErr_Clear();
 		}
 	    }
-	    if (widename == NULL) 
+	    if (widename == NULL)
 #endif
 	    {
-		if (!PyArg_ParseTupleAndKeywords(args, kwds, "et|s:fileio",
+		if (!PyArg_ParseTupleAndKeywords(args, kwds, "et|si:fileio",
 						 kwlist,
 						 Py_FileSystemDefaultEncoding,
-						 &name, &mode))
+						 &name, &mode, &closefd))
 			goto error;
 	    }
 	}
@@ -237,8 +247,16 @@ fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 
 	if (fd >= 0) {
 		self->fd = fd;
+		self->closefd = closefd;
 	}
 	else {
+		self->closefd = 1;
+		if (!closefd) {
+			PyErr_SetString(PyExc_ValueError,
+                            "Cannot use closefd=True with file name");
+			goto error;
+		}
+
 		Py_BEGIN_ALLOW_THREADS
 		errno = 0;
 #ifdef MS_WINDOWS
@@ -270,7 +288,7 @@ fileio_dealloc(PyFileIOObject *self)
 	if (self->weakreflist != NULL)
 		PyObject_ClearWeakRefs((PyObject *) self);
 
-	if (self->fd >= 0) {
+	if (self->fd >= 0 && self->closefd) {
 		errno = internal_close(self);
 		if (errno < 0) {
 #ifdef HAVE_STRERROR

Objects/fileobject.c

@@ -27,15 +27,15 @@ extern "C" {
 
 PyObject *
 PyFile_FromFd(int fd, char *name, char *mode, int buffering, char *encoding,
-	      char *newline)
+	      char *newline, int closefd)
 {
 	PyObject *io, *stream, *nameobj = NULL;
 
 	io = PyImport_ImportModule("io");
 	if (io == NULL)
 		return NULL;
-	stream = PyObject_CallMethod(io, "open", "isiss", fd, mode,
-				     buffering, encoding, newline);
+	stream = PyObject_CallMethod(io, "open", "isissi", fd, mode,
+				     buffering, encoding, newline, closefd);
 	Py_DECREF(io);
 	if (stream == NULL)
 		return NULL;

Python/import.c

@@ -2588,7 +2588,7 @@ call_find_module(char *name, PyObject *path)
 				   (char*)PyUnicode_GetDefaultEncoding();
 		}
 		fob = PyFile_FromFd(fd, pathname, fdp->mode, -1,
-					(char*)encoding, NULL);
+				    (char*)encoding, NULL, 1);
 		if (fob == NULL) {
 			close(fd);
 			PyMem_FREE(found_encoding);

Python/pythonrun.c

@@ -720,7 +720,7 @@ initstdio(void)
 
 	/* Set sys.stdin */
 	if (!(std = PyFile_FromFd(fileno(stdin), "<stdin>", "r", -1,
-				      NULL, "\n"))) {
+				  NULL, "\n", 0))) {
 		goto error;
 	}
 	PySys_SetObject("__stdin__", std);
@@ -729,16 +729,16 @@ initstdio(void)
 
 	/* Set sys.stdout */
 	if (!(std = PyFile_FromFd(fileno(stdout), "<stdout>", "w", -1,
-				      NULL, "\n"))) {
+				  NULL, "\n", 0))) {
             goto error;
         }
 	PySys_SetObject("__stdout__", std);
 	PySys_SetObject("stdout", std);
 	Py_DECREF(std);
 
-	/* Set sys.stderr */
+	/* Set sys.stderr, replaces the preliminary stderr */
 	if (!(std = PyFile_FromFd(fileno(stderr), "<stderr>", "w", -1,
-				      NULL, "\n"))) {
+				  NULL, "\n", 0))) {
             goto error;
         }
         PySys_SetObject("__stderr__", std);