It seems like an oversight of the author, though it is not clear why this happily compiles with clang 3.4.1 on FreeBSD 10.4-STABLE and GCC on RHEL6.

The error is (HP-UX 11.31 and HP C/aC++ B3910B A.06.28.03 [Dec 13 2016]):

/opt/aCC/bin/cc -Ae +z -O -I./Include -I. -I/usr/local/include -I/var/osipovmi/cpython/Include -I/var/osipovmi/cpython -c /var/osipovmi/cpython/Modules/selectmodule.c -o build/temp.hp-ux-B.11.31-ia64-3.8-pydebug/var/osipovmi/cpython/Modules/selectmodule.o
"/var/osipovmi/cpython/Modules/selectmodule.c", line 412: warning bpo-4232-D:
conversion from "PyObject *" to a more strictly aligned type
"PyDictObject *" may cause misaligned access
self->ufd_len = PyDict_GET_SIZE(self->dict);
^

"/var/osipovmi/cpython/Modules/selectmodule.c", line 849: error bpo-2130:
expected a "{"
static PyObject *
^

"/var/osipovmi/cpython/Modules/selectmodule.c", line 898: error bpo-2101:
"timeout_obj" has already been declared in the current scope
PyObject *result_list = NULL, *timeout_obj = NULL;
^

2 errors detected in the compilation of "/var/osipovmi/cpython/Modules/selectmodule.c".

caused by:

+static PyObject *
+select_devpoll_modify_impl(devpollObject *self, int fd,

•                       unsigned short eventmask)
  

+/[clinic end generated code: output=bc2e6d23aaff98b4 input=f0d7de3889cc55fb]/
static PyObject *
devpoll_modify(devpollObject *self, PyObject *args)
{

• return internal_devpoll_register(self, args, 1);

• return internal_devpoll_register(self, fd, eventmask, 1);
  }

Signature change, but prototype has not been changed.

static PyObject *
-poll_poll(pollObject *self, PyObject *args)
+select_poll_poll_impl(pollObject *self, PyObject *timeout_obj)
+/[clinic end generated code: output=876e837d193ed7e4 input=7a446ed45189e894]/
{

• PyObject *result_list = NULL, *timeout_obj = NULL;

• PyObject *result_list = NULL;
  int poll_result, i, j;
  PyObject *value = NULL, *num = NULL;
  _PyTime_t timeout = -1, ms = -1, deadline = 0;
  int async_err = 0;

• if (!PyArg_ParseTuple(args, "|O:poll", &timeout_obj)) {

•    return NULL;
  

• }
• if (timeout_obj != NULL && timeout_obj != Py_None) {

• if (timeout_obj != Py_None) {

timeout_obj has been added to the function signature, but the internal NULL assignment has not been removed.

A PR is in preparation.

New changeset 0e6e7a1 by Tal Einat (Michael Osipov) in branch 'master':
bpo-34419: selectmodule.c does not compile on HP-UX due to bpo-31938 (GH-8796)
0e6e7a1

Michael, thanks for catching this and supplying a PR!

Bevakasha!