Re: [Swig-user] stl algorithms for stl containers/iterators of python objects

[William S F. <ws...@fu...>]

Eric Mahurin wrote:
> I'm trying to setup a generic python module that wraps the bulk of C++
> STL for use in python with normal python objects.  So far, I've been
> able to wrap containers/iterators quite well.  Here's what I'm using:
> 
> %module stl
> 
> %include <std_container.i>
> 
> %include <std_vector.i>
> %include <std_deque.i>
> %include <std_list.i>
> %include <std_set.i>
> %include <std_map.i>
> %include <std_multiset.i>
> %include <std_multimap.i>
> 
> %template(_vector  ) std::vector  <swig::PyObject_ptr>;
> %template(_deque   ) std::deque   <swig::PyObject_ptr>;
> %template(_list    ) std::list    <swig::PyObject_ptr>;
> %template(_set     ) std::set     <swig::PyObject_ptr>;
> %template(_map     ) std::map     <swig::PyObject_ptr,swig::PyObject_ptr>;
> %template(_multiset) std::multiset<swig::PyObject_ptr>;
> %template(_multimap) std::multimap<swig::PyObject_ptr,swig::PyObject_ptr>;
> 
> %pythoncode %{
>     vector   = _vector 
>     deque    = _deque  
>     list     = _list   
>     set      = _set    
>     map      = _map    
>     multiset = _multiset
>     multimap = _multimap
> %}
> 
> After creating this module, I can use the classes vector, deque, etc
> from this module with both python (i.e. __iter__ and append) and C++
> (i.e. begin/end and push_back) method names.  These containers also hold
> generic python objects.  Very nice.
> 
> There are a few other data structures I would also like too see: slist,
> priority_queue, hash_set, hash_map.  But, the major ones I wanted are
> listed above - set and map.  Those give me ordered sequences with
> O(log(n)) performance - usually implemented with red-black trees.  There
> is no performance equivalent of this in standard python.
> 
> The major category missing from this STL module above is the
> "algorithms".  I specifically would like stuff from the sorting
> category: nth_element and *_heap since priority_queue isn't ready for
> swig yet.
> 
> Can anbody get me started by showing me how to port the STL algorithm
> nth_element over to python using iterators to STL containers containing
> python objects (from above)?
> 

You should tackle this like any other templated code you want to use
from SWIG. So giving the following to SWIG would be a start...

namespace std {
template <class RandomAccessIterator>
void nth_element(RandomAccessIterator first, RandomAccessIterator nth,
                 RandomAccessIterator last);
}

then you need a %template for RandomAccessIterator. I don't know the
Python STL iterator mappings at all, so this might be covered already.
If not you need to get the RandomAccessIterator from the C++ world into
Python, by either using one of the Python STL wrappers (eg
vector::begin()) or write a method that will return it for you.

If I had more knowledge on the Python STL wrappers or loads of time, I'd
write some code, but I'm afraid you're going to have to experiment yourself.

William