[C++-sig] Re: implicitly_convertible

[David Abrahams]

"aashish" <aashish at vrac.iastate.edu> writes:

> Hi, 
>
> I wanted to have a function like this where when I pass a list I will either
> get return as set of integers or std::vector of double. 
>
> I tried to implement the function in this manner .....
>
> C++--------------------------------
> int make_vector(bp::list vlist)
> {
> 	//std::vector<double> vector_list;
> 	int k = extract<int>(vlist.attr("__len__")());	
> 	
> 	/*for (int i=0;i<10;i++)
> 	{
> 	
> vector_list.push_back(extract<double>(lt.attr("__getitem__")(i)));

That's the hard/ugly way.

Why not:  

          vector_list.push_back(extract<double>(lt[i]));

??

> 	}
>
> 	return vector_list;*/
> 	
> 	int kk = extract<int>(vlist.attr("__getitem__")(0));
> 	
> 	return kk;
> }
> Python-----------------------------
>
> L = ['1','2','3']
> a = make_vector(L)
> print a
>
> The problem is that I am getting the correct value for 'k' here but then it
> does throws error saying that 
>
> Tracekack(most recent call last)
> File "pytest2.py" , line 30, in ?
> 	A = "make.vector"(L)
        ^^^^^^^^^^^^^
I can't believe that you copied this error message correctly.

> Typeerror: No registered converter was able to produce a C++ rvalue of type
> int from this Python object of type str. 
>
> Now what does this error mean?? 

The error means that you tried to extract<int> from a Python string
object.

> And How can sole this problem. 

Store ints instead of strings in L

  L = [ 1, 2, 3 ]

??
-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com