bpo-39099: add scandir.dirfd()

Doc/library/os.rst

@@ -2218,6 +2218,14 @@ features:
    The :func:`scandir` iterator supports the :term:`context manager` protocol
    and has the following method:
 
+   .. method:: scandir.dirfd()
+
+      Return directory file descriptor.
+
+      .. versionadded:: 3.9
+
+      .. availability:: POSIX
+
    .. method:: scandir.close()
 
       Close the iterator and free acquired resources.

Doc/whatsnew/3.9.rst

@@ -169,6 +169,9 @@ Exposed the Linux-specific :func:`os.pidfd_open` (:issue:`38692`) and
 :data:`os.P_PIDFD` (:issue:`38713`) for process management with file
 descriptors.
 
+Added :meth:`~os.scandir.dirfd` method.
+(Contributed by Giampaolo Rodola in :issue:`39099`)
+
 threading
 ---------
 

Lib/test/test_os.py

@@ -4001,6 +4001,13 @@ def test_resource_warning(self):
         with self.check_no_resource_warning():
             del iterator
 
+    def test_dirfd(self):
+        with os.scandir('.') as itr:
+            if not hasattr(itr, 'dirfd'):
+                self.skipTest("not supported")
+            self.assertGreater(itr.dirfd(), 0)
+        self.assertRaises(ValueError, itr.dirfd)
+
 
 class TestPEP519(unittest.TestCase):
 

Misc/NEWS.d/next/Library/2019-12-19-19-37-01.bpo-39099.bZ8tpO.rst

@@ -0,0 +1,2 @@
+os.scandir() object has a new dirfd() method.  (patch contributed by
+Giampaolo Rodola)

Modules/posixmodule.c

@@ -13180,6 +13180,23 @@ ScandirIterator_close(ScandirIterator *self, PyObject *args)
     Py_RETURN_NONE;
 }
 
+#ifdef HAVE_DIRFD
+static PyObject *
+ScandirIterator_dirfd(ScandirIterator *self, PyObject *args)
+{
+    int fd;
+
+    if (ScandirIterator_is_closed(self)) {
+        PyErr_SetString(PyExc_ValueError, "I/O operation on closed directory");
+        return NULL;
+    }
+    fd = dirfd(self->dirp);
+    if (fd == -1)
+        return path_error(&self->path);
+    return Py_BuildValue("i", fd);
+}
+#endif  /* HAVE_DIRFD */
+
 static PyObject *
 ScandirIterator_enter(PyObject *self, PyObject *args)
 {
@@ -13235,6 +13252,9 @@ ScandirIterator_dealloc(ScandirIterator *iterator)
 static PyMethodDef ScandirIterator_methods[] = {
     {"__enter__", (PyCFunction)ScandirIterator_enter, METH_NOARGS},
     {"__exit__", (PyCFunction)ScandirIterator_exit, METH_VARARGS},
+#ifdef HAVE_DIRFD
+    {"dirfd", (PyCFunction)ScandirIterator_dirfd, METH_NOARGS},
+#endif
     {"close", (PyCFunction)ScandirIterator_close, METH_NOARGS},
     {NULL}
 };