os.sendfile(headers=None, trailers=None) arguments are not actually accepted

Needs to be tested on a BSD.

Doc/library/os.rst

@@ -1072,7 +1072,7 @@ or `the MSDN <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Window
 
 
 .. function:: sendfile(out, in, offset, count)
-              sendfile(out, in, offset, count, headers=None, trailers=None, flags=0)
+              sendfile(out, in, offset, count, [headers], [trailers], flags=0)
 
    Copy *count* bytes from file descriptor *in* to file descriptor *out*
    starting at *offset*.

Lib/test/test_os.py

@@ -2170,7 +2170,7 @@ class TestSendfile(unittest.TestCase):
             **{'in': self.fileno})
         if self.SUPPORT_HEADERS_TRAILERS:
             os.sendfile(self.sockno, self.fileno, offset=0, count=4096,
-                headers=None, trailers=None, flags=0)
+                headers=(), trailers=(), flags=0)
 
     # --- headers / trailers tests
 

Modules/posixmodule.c

@@ -8246,7 +8246,7 @@ posix_write(PyObject *self, PyObject *args)
 #ifdef HAVE_SENDFILE
 PyDoc_STRVAR(posix_sendfile__doc__,
 "sendfile(out, in, offset, count) -> byteswritten\n\
-sendfile(out, in, offset, count, headers=None, trailers=None, flags=0)\n\
+sendfile(out, in, offset, count[, headers][, trailers], flags=0)\n\
             -> byteswritten\n\
 Copy count bytes from file descriptor in to file descriptor out.");
 
@@ -8286,7 +8286,7 @@ posix_sendfile(PyObject *self, PyObject *args, PyObject *kwdict)
     if (headers != NULL) {
         if (!PySequence_Check(headers)) {
             PyErr_SetString(PyExc_TypeError,
-                "sendfile() headers must be a sequence or None");
+                "sendfile() headers must be a sequence");
             return NULL;
         } else {
             Py_ssize_t i = 0; /* Avoid uninitialized warning */
@@ -8303,7 +8303,7 @@ posix_sendfile(PyObject *self, PyObject *args, PyObject *kwdict)
     if (trailers != NULL) {
         if (!PySequence_Check(trailers)) {
             PyErr_SetString(PyExc_TypeError,
-                "sendfile() trailers must be a sequence or None");
+                "sendfile() trailers must be a sequence");
             return NULL;
         } else {
             Py_ssize_t i = 0; /* Avoid uninitialized warning */