pyconversions.h

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/* -*- mode:c++ -*- */

#ifndef PY_CONVERSIONS_H
#define PY_CONVERSIONS_H

// include first to avoid _POSIX_C_SOURCE redefined warnings
#include <boost/python.hpp>

#include <vector>


using namespace boost::python;

  template < typename ContainerType >
  struct to_tuple
  {
    static PyObject* convert (ContainerType const& c)
    {
      using boost::python::incref; // works around gcc 2.96 bug
      using boost::python::list; // ditto 
      list result;
      typename ContainerType::const_iterator i = c.begin();
      for( ; i != c.end(); ++i)
        {
          result.append(*i);
        }
      return incref(tuple(result).ptr());
    }
  };

  template < typename T >
  struct std_vector_to_tuple 
  {
    std_vector_to_tuple ()
    {
      to_python_converter < std::vector < T >, 
                            to_tuple < std::vector < T > >  > ();
    }
  };

  struct default_policy
  {
    static bool check_convertibility_per_element() { return false; }

    template <typename ContainerType>
    static bool check_size(boost::type<ContainerType>, std::size_t /* sz */ )
    {
      return true;
    }

    template <typename ContainerType>
    static void 
    assert_size(boost::type<ContainerType>, std::size_t /* sz */) {}

    template <typename ContainerType>
    static void reserve(ContainerType& a, std::size_t /* sz */ ) {}
  };

  struct variable_capacity_policy : default_policy
  {
    template <typename ContainerType>
    static void reserve(ContainerType& a, std::size_t sz)
    {
      a.reserve(sz);
    }

    template <typename ContainerType, typename ValueType>
    static void set_value(ContainerType& a, std::size_t i, ValueType const& v)
    {
      assert(a.size() == i);
      a.push_back(v);
    }
  };

  template <typename ContainerType, typename ConversionPolicy>
  struct from_python_sequence
  {
    typedef typename ContainerType::value_type container_element_type;

    from_python_sequence()
    {
      boost::python::converter::registry::push_back(
        &convertible,
        &construct,
        boost::python::type_id<ContainerType>());
    }

    static void* convertible(PyObject* obj_ptr)
    {
      using namespace boost::python;
      using boost::python::allow_null; // works around gcc 2.96 bug
      {
        // Restriction to list, tuple, iter, xrange until
        // Boost.Python overload resolution is enhanced.
         //
         // add PySequence_Check() for numarray.
         //
         if (!(   PyList_Check(obj_ptr)
                  || PyTuple_Check(obj_ptr)
                  || PyIter_Check(obj_ptr)
                  || PyRange_Check(obj_ptr)
                  || PySequence_Check(obj_ptr) )) return 0;
      }
      handle<> obj_iter(allow_null(PyObject_GetIter(obj_ptr)));
      if (!obj_iter.get()) { // must be convertible to an iterator
        PyErr_Clear();
        return 0;
      }
      if (ConversionPolicy::check_convertibility_per_element()) {
        int obj_size = PyObject_Length(obj_ptr);
        if (obj_size < 0) { // must be a measurable sequence
          PyErr_Clear();
          return 0;
        }
        if (!ConversionPolicy::check_size(
          boost::type<ContainerType>(), obj_size)) return 0;
        bool is_range = PyRange_Check(obj_ptr);
        //std::size_t i=0;
                int i = 0;
#ifndef _MSC_VER // because it causes c1001: internal compiler error
        for(;;i++) {
          handle<> py_elem_hdl(allow_null(PyIter_Next(obj_iter.get())));
          if (PyErr_Occurred()) {
            PyErr_Clear();
            return 0;
          }
          if (!py_elem_hdl.get()) break; // end of iteration
          object py_elem_obj(py_elem_hdl);
          extract<container_element_type> elem_proxy(py_elem_obj);
          if (!elem_proxy.check()) return 0;
          if (is_range) break; // in a range all elements are of the same type
        }
        if (!is_range) assert(i == obj_size );
#endif
      }
      return obj_ptr;
    }

    static void construct(
      PyObject* obj_ptr,
      boost::python::converter::rvalue_from_python_stage1_data* data)
    {
      using namespace boost::python;
      using boost::python::allow_null; // works around gcc 2.96 bug
      using boost::python::converter::rvalue_from_python_storage; // dito
      using boost::python::throw_error_already_set; // dito
      handle<> obj_iter(PyObject_GetIter(obj_ptr));
      void* storage = (
        (rvalue_from_python_storage<ContainerType>*)
          data)->storage.bytes;
      new (storage) ContainerType();
      data->convertible = storage;
      ContainerType& result = *((ContainerType*)storage);
      std::size_t i=0;
      for(;;i++) {
        handle<> py_elem_hdl(allow_null(PyIter_Next(obj_iter.get())));
        if (PyErr_Occurred()) throw_error_already_set();
        if (!py_elem_hdl.get()) break; // end of iteration
        object py_elem_obj(py_elem_hdl);
        extract<container_element_type> elem_proxy(py_elem_obj);
        ConversionPolicy::set_value(result, i, elem_proxy());
      }
      ConversionPolicy::assert_size(boost::type<ContainerType>(), i);
    }

  };

#endif // PY_CONVERSIONS_H