gh-155621: Fix unrepresentable defaults in socket.sendmsg() signature (#155623)

Lib/test/test_inspect/test_inspect.py

@@ -6340,7 +6340,7 @@ class TestSignatureDefinitions(unittest.TestCase):
         # depends on the number of the arguments.
         methods_no_signature = {'ioctl', 'sendto', 'setsockopt'}
         # These have parameters with unrepresentable default values.
-        methods_unsupported_signature = {'listen', 'sendmsg', 'sendmsg_afalg'}
+        methods_unsupported_signature = {'listen', 'sendmsg_afalg'}
         defined = vars(socket.SocketType).keys()
         self._test_module_has_signatures(socket,
                 no_signature, unsupported_signature,

Modules/clinic/socketmodule.c.h

@@ -1018,8 +1018,7 @@ exit:
 #if defined(CMSG_LEN)
 
 PyDoc_STRVAR(_socket_socket_sendmsg__doc__,
-"sendmsg($self, buffers, ancdata=<unrepresentable>, flags=0,\n"
-"        address=<unrepresentable>, /)\n"
+"sendmsg($self, buffers, ancdata=(), flags=0, address=None, /)\n"
 "--\n"
 "\n"
 "Send normal and ancillary data to the socket.\n"
@@ -2479,4 +2478,4 @@ exit:
 #ifndef _SOCKET_CMSG_SPACE_METHODDEF
     #define _SOCKET_CMSG_SPACE_METHODDEF
 #endif /* !defined(_SOCKET_CMSG_SPACE_METHODDEF) */
-/*[clinic end generated code: output=133662a8c304b1b7 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=acc30d6fdeb54e90 input=a9049054013a1b77]*/

Modules/socketmodule.c

@@ -4990,9 +4990,9 @@ sock_sendmsg_impl(PySocketSockObject *s, void *data)
 _socket.socket.sendmsg
     self as s: self(type="PySocketSockObject *")
     buffers as data_arg: object
-    ancdata as cmsg_arg: object = NULL
+    ancdata as cmsg_arg: object(c_default="NULL") = ()
     flags: int = 0
-    address as addr_arg: object = NULL
+    address as addr_arg: object(c_default="NULL") = None
     /
 
 Send normal and ancillary data to the socket.
@@ -5016,7 +5016,7 @@ static PyObject *
 _socket_socket_sendmsg_impl(PySocketSockObject *s, PyObject *data_arg,
                             PyObject *cmsg_arg, int flags,
                             PyObject *addr_arg)
-/*[clinic end generated code: output=3b4cb1110644ce39 input=8ae408971a3aa329]*/
+/*[clinic end generated code: output=3b4cb1110644ce39 input=5fdf9b49bed3848b]*/
 
 {
     Py_ssize_t i, ndatabufs = 0, ncmsgs, ncmsgbufs = 0;