Re: [pygccxml-development] How to return a std::vector<std::string> to Python

[Roman Y. <rom...@gm...>]

On Wed, Sep 10, 2008 at 6:08 PM,  <bf...@co...> wrote:
> Hi,
>
> also after lengthy search on the net I could not find a working example for the following (probably common)  use case:
>
> I would like to expose a C++ function to Python which has as result type
>    std::vector<std::string>
>
> When invoking the exposed function from Python I get the message
>
>  File "test.py", line 15, in <module>
>    v = a.alias_to_account_list(al)
> TypeError: No to_python (by-value) converter found for C++ type: std::vector<std::string, std::allocator<std::string> >
>
> The function looks as follows:
>  vector<string> alias_to_account_list(string ali="SAP") {
>      set<string> accts = _tlib2->alias_to_account_list(ali);
>      cerr << "alias '" << ali << "' expands to that many accounts::" << accts.size() << endl;
>      copy(accts.begin(), accts.end(), ostream_iterator<string>(cerr, ","));
>      vector<string> res;
>      copy(accts.begin(), accts.end(), back_inserter(res));
>      return res;
>  }
>
> What can I do? Is there a way to construct native Python objects? Interestingly my code works when I return
>    std::vector<int>
>
> In this case I can access the elements of the vector from python with the [] notation. The object is no native python array, however, which I would prefer.
> I am only interested in return by value at this point, so I do not want to change the C++ vector from Python.
>
> This is what I want to do in Python:
>
>   for al in ["MAN","LHA","SIE25"]:
>       v = a.alias_to_account_list(al)
>       print "dir(v)= ",dir(v), len(v),v[0],v[1],v[2]
>
> Any hints are appreciated,

What indexing suite do you use?
If you use indexing suite that comes with boost.python than the
following code will register your vector correctly:

typedef std::vector< std::string > strings_t;



inline void do_nothing( const strings_t& ){}



inline strings_t get_names(){...}

namespace bp = boost::python;

typedef bp::class_< std::vector< std::string > > strings_t_exposer_t;
strings_t_exposer_t strings_t_exposer = strings_t_exposer_t(
"strings_t", "documentation" );
bp::scope strings_t_scope( strings_t_exposer );
strings_t_exposer.def( bp::vector_indexing_suite< ::std::vector<
std::string >, true >() );

Py++ should be able to generate the correct code, if not show me your
use case - I will improve it.

HTH

-- 
Roman Yakovenko
C++ Python language binding
http://www.language-binding.net/