[C++-sig] checking passed arg is python type

[Jim Bosch]

On 03/14/2013 06:12 PM, Neal Becker wrote:
> I'm expecting a numpy.random.RandomState object to be passed to me.  I want to
> check it is.  The best I could think of is below.  Anything more boost::python-
> ish to do this task?
>
> static object rs_obj;
>
> template<typename out_type=uint32_t>
> struct engine {
>    typedef out_type result_type;
>    bp::object rs;		// RandomState object
>
>    void verify (object const& o) {
>      if (!PyObject_IsInstance(o.ptr(), rs_obj.ptr()))
>        throw std::runtime_error ("engine: expected RandomState");
>    }
>
>    engine (bp::object const& _rs) : rs (_rs) { verify (_rs); }
> ...
>
> BOOST_PYTHON_MODULE...
>
>    object mod = object (handle<> ((PyImport_ImportModule("numpy.random"))));
>    rs_obj = mod.attr("RandomState");
>

I believe you can replace the penultimate line with:

bp::object mod = bp::import("numpy.random");

But I can't think of any ways to Boost.Python-ize the rest; there really should be an "isinstance" wrapper in Boost.Python, but there isn't.  You may also want to be a little careful with the return value of PyObject_IsInstance - I believe that it's psosible for it to raise an exception instead of simply returning 0, and in that case you'd want to use bp::throw_error_already_set() to propagate the exception to Python.


Jim