[C++-sig] Boost-python wrapping a vector of vectors?

[Tim Couper]

Ah I understand .. so will reply to my own posting for others new to pb ...

C++ constructors with one argument behave differently I understand, so 
taking a 2 argument case:

class A
{
public
    A(int i, const std::vector<std::vector double >>& my_array);
};


In the BOOST_PYTHON_MODULE(foo)  ..

define a type using typedef:

     typedef std::vector<std::vector<double> > double_trouble;

and add the python wrappers we're going to need - one for wrapping a 
vector of doubles, and one for the vector of vectors ..

     class_<std::vector<std::vector<double> > > ("v2_double")
         .def(vector_indexing_suite<std::vector<std::vector<double> > >());

     class_<std::vector<double> > ("v_double")
         .def(vector_indexing_suite<std::vector<double> >());

now define the constructor like Troy said ..

     class_<duh::A>("A")
         .def(init<int, double_trouble >())
         ;


bjam this lot and we then can write out nosetest tests:

def test_v_double():
     v = foo.v_double()
     v[:] = [1.4,2.5]
     assert_equals(len(v),2)
     assert_almost_equal(v[0],1.4)


def test_v2_double():
     v2 = foo.v2_double()
     v1a = foo.v_double()
     v2a = foo.v_double()
     v1a[:] = [1.4, 2.5, 5.6]
     v2a[:] = [3.4, 2.8, 7.8, 12.5]

     v2[:] = [v1a,v2a]
     assert_equals(len(v2),2)
     assert_almost_equal(v2[0][0],1.4)

def test_A():
     v2 = foo.v2_double()
     v1a = foo.v_double()
     v2a = foo.v_double()
     v1a[:] = [1.4, 2.5, 5.6]
     v2a[:] = [3.4, 2.8, 7.8, 12.5]

     v2[:] = [v1a,v2a]
     res = foo.A(1, v2)
     assert isinstance(res, foo.A)

and there we have it ..

I'll be back ... :-)

Tim

On 07/01/2010 09:21, Tim Couper wrote:
> Troy
>
> Thanks for the prompt reply .. I'm a python expert and a C++ novice 
> ... Apologies for not getting this ...
>
> I've seen I can define a python mapping using the vector_indexing suite
>
> class_< std::vector< std::vector<double> > >("vector_double2")
>      .def(vector_indexing_suite<std::vector< std::vector<double> > >
>
> but I can't see how to get that information into the init argument in 
> the C++
>
> class_<A>("A")
>     .def(init<vector_double2>( ))
>
> as vector_double2 isn't known when the c++ compiles, so this clearly 
> isn't the "type" argument to which you refer. Clearly there's 
> something I'm missing. How do I define a type? Should I be using the 
> named constructors/factories described in 
> http://wiki.python.org/moin/boost.python/HowTo? If so how?
>
> Thanks again
>
> Tim
>
>
>
>
>
>
> On 06/01/2010 23:16, troy d. straszheim wrote:
>> Tim Couper wrote:
>>>
>>> I'm trying to boost-python a vector-of-vectors, like
>>>
>>> class A
>>> {
>>> public
>>>    A(const std::vector<std::vector double >>& my_array);
>>> };
>>>
>>> and would intuitively write the wrapper:
>>>
>>> BOOST_PYTHON_MODULE(foo)
>>> {
>>> using namespace boost::python
>>>
>>> class_<A>("A")
>>>     .def(init(std::vector<std::vector<double> >())
>>>     ;
>>>
>>> but get the error "a call to a constructor cannot appear in a 
>>> constant expression"
>>
>> Syntax error, init takes a type argument:  init<T>()
>>
>> -t
>>
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