Re: [Discuss-gnuradio] vectors of vectors in python

[Eric Blossom]

On Wed, Feb 07, 2007 at 10:31:05AM -0500, Michael Dickens wrote:
> On Feb 1, 2007, at 11:47 PM, Achilleas Anastasopoulos wrote:
> >private:
> >  std::vector< std::vector<int> > d_PS;
> >public:
> >  const std::vector< std::vector<int> > & PS () const { return d_PS; }
> 
> Here's a quick, partial answer.  According to the SWIG docs &  
> tutorials, what one needs to do is something like (these could be in  
> struct's of class'es instead):
> 
> typedef std::vector<int> VecInt;
> typedef std::vector<VecInt> VecInt2;
> 
> Then in Python (after compilation via SWIG -> C++), something like:
> 
> >>> import VecStuff
> >>> a = VecInt ([1 2 3])
> >>> b = VecInt ([4 5 6])
> >>> c = VecInt2 (a, b)
> 
> Please note that 'a' and 'b' above do -not- need to be the same  
> length, not for C++ nor SWIG nor Python, since this is not a "matrix"  
> but just a vector of vectors.
> 
> The exact details remain to be figured out.  The basic idea is that,  
> in order for SWIG (and thus Python) to know what type of structure is  
> being dealt with, one has to name all of the relevant parts of the  
> structure.  Thus
> 
> std::vector< std::vector<int> > V2Int;
> 
> won't work because SWIG can't name the internal "std::vector<int>"  
> data.  SWIG takes the approach of "separate and conquer".  Hope this  
> helps! - MLD

Note that std::vector<int>, <gr_complex>, <float> and more are already
handled in gnuradio.i

You may be missing only a template instantiate in the .i file to have

  const std::vector< std::vector<int> >

work.

You may want to call it

  const std::vector< const std::vector<int> >
  
In that case, swig may just "do the right thing" and automatically
generate the correct typemap since it's free to create new copies of
the nested vectors.  I would expect (but haven't tested)  that this
would allow you to call from python using syntax like this:

  foo(((1,2,3), (4,5,6), (7,8,9,10)))

Eric