ns-3.25 fails to build on an Ubuntu 16.04 (gcc-5.3.1, python 3.5.1) system when Python-3.5 is used.  

To reproduce, unpack the ns-allinone-3.25 release, cd into ns-3.25, and run:

./waf configure

make sure that Python bindings are 'enabled', then run:

./waf build

The error is:

src/fd-net-device/bindings/ns3module.cc:2078:1: error: invalid conversion from ‘cmpfunc {aka void*}’ to ‘PyAsyncMethods*’ [-fpermissive]
 };

(although this can be observed also in other modules such as wimax; it depends on compilation order).   

That part of the ns3module.cc file generated by python-3.5 is:

PyTypeObject PyNs3FdNetDeviceHelper_Type = {
    PyVarObject_HEAD_INIT(NULL, 0)
    (char *) "fd_net_device.FdNetDeviceHelper",            /* tp_name */
    sizeof(PyNs3FdNetDeviceHelper),                  /* tp_basicsize */
    0,                                 /* tp_itemsize */
    /* methods */
    (destructor)_wrap_PyNs3FdNetDeviceHelper__tp_dealloc,        /* tp_dealloc */
    (printfunc)0,                      /* tp_print */
    (getattrfunc)NULL,       /* tp_getattr */
    (setattrfunc)NULL,       /* tp_setattr */
    (cmpfunc)NULL,           /* tp_compare */
    (reprfunc)NULL,             /* tp_repr */
    (PyNumberMethods*)NULL,     /* tp_as_number */


The cmpfunc related to tp_compare is the one the compiler is complaining about.  Note that Python 3.5 documentation states:

  PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
                                    or tp_reserved (Python 3) */

I can confirm that this problem is only with Python 3.5 and not 3.4