from_python.cpp

C++的一个好库。。。现在很流行

// Copyright David Abrahams 2002.
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

#include <boost/python/converter/from_python.hpp>
#include <boost/python/converter/registrations.hpp>
#include <boost/python/converter/rvalue_from_python_data.hpp>

#include <boost/python/object/find_instance.hpp>

#include <boost/python/handle.hpp>
#include <boost/python/detail/raw_pyobject.hpp>
#include <boost/python/cast.hpp>

#include <vector>
#include <algorithm>

namespace boost { namespace python { namespace converter { 

// rvalue_from_python_stage1 -- do the first stage of a conversion
// from a Python object to a C++ rvalue.
//
//    source     - the Python object to be converted
//    converters - the registry entry for the target type T
//
// Postcondition: where x is the result, one of:
//
//   1. x.convertible == 0, indicating failure
//
//   2. x.construct == 0, x.convertible is the address of an object of
//      type T. Indicates a successful lvalue conversion
//
//   3. where y is of type rvalue_from_python_data<T>,
//      x.construct(source, y) constructs an object of type T
//      in y.storage.bytes and then sets y.convertible == y.storage.bytes,
//      or else throws an exception and has no effect.
BOOST_PYTHON_DECL rvalue_from_python_stage1_data rvalue_from_python_stage1(
    PyObject* source
    , registration const& converters)
{
    rvalue_from_python_stage1_data data;

    // First check to see if it's embedded in an extension class
    // instance, as a special case.
    data.convertible = objects::find_instance_impl(source, converters.target_type, converters.is_shared_ptr);
    if (data.convertible)
    {
        data.construct = 0;
    }
    else
    {
        for (rvalue_from_python_chain const* chain = converters.rvalue_chain;
             chain != 0;
             chain = chain->next)
        {
            void* r = chain->convertible(source);
            if (r != 0)
            {
                data.convertible = r;
                data.construct = chain->construct;
                break;
            }
        }
    }
    return data;
}

// rvalue_result_from_python -- return the address of a C++ object which
// can be used as the result of calling a Python function.
//
//      src  - the Python object to be converted
//
//      data - a reference to the base part of a
//             rvalue_from_python_data<T> object, where T is the
//             target type of the conversion.
//
// Requires: data.convertible == &registered<T>::converters
//
BOOST_PYTHON_DECL void* rvalue_result_from_python(
    PyObject* src, rvalue_from_python_stage1_data& data)
{
    // Retrieve the registration
    // Cast in two steps for less-capable compilers
    void const* converters_ = data.convertible;
    registration const& converters = *static_cast<registration const*>(converters_);

    // Look for an eligible converter
    data = rvalue_from_python_stage1(src, converters);
    return rvalue_from_python_stage2(src, data, converters);
}

BOOST_PYTHON_DECL void* rvalue_from_python_stage2(
    PyObject* source, rvalue_from_python_stage1_data& data, registration const& converters)
{
    if (!data.convertible)
    {
        handle<> msg(
            ::PyString_FromFormat(
                "No registered converter was able to produce a C++ rvalue of type %s from this Python object of type %s"
                , converters.target_type.name()
                , source->ob_type->tp_name
                ));
              
        PyErr_SetObject(PyExc_TypeError, msg.get());
        throw_error_already_set();
    }

    // If a construct function was registered (i.e. we found an
    // rvalue conversion), call it now.
    if (data.construct != 0)
        data.construct(source, &data);

    // Return the address of the resulting C++ object
    return data.convertible;
}

BOOST_PYTHON_DECL void* get_lvalue_from_python(
    PyObject* source
    , registration const& converters)
{
    // Check to see if it's embedded in a class instance
    void* x = objects::find_instance_impl(source, converters.target_type);
    if (x)
        return x;

    lvalue_from_python_chain const* chain = converters.lvalue_chain;
    for (;chain != 0; chain = chain->next)
    {
        void* r = chain->convert(source);
        if (r != 0)
            return r;
    }
    return 0;
}

namespace
{
  // Prevent looping in implicit conversions. This could/should be
  // much more efficient, but will work for now.
  typedef std::vector<rvalue_from_python_chain const*> visited_t;
  static visited_t visited;

  inline bool visit(rvalue_from_python_chain const* chain)
  {
      visited_t::iterator const p = std::lower_bound(visited.begin(), visited.end(), chain);
      if (p != visited.end() && *p == chain)
          return false;
      visited.insert(p, chain);
      return true;
  }

  // RAII class for managing global visited marks.
  struct unvisit
  {
      unvisit(rvalue_from_python_chain const* chain)
          : chain(chain) {}
      
      ~unvisit()
      {
          visited_t::iterator const p = std::lower_bound(visited.begin(), visited.end(), chain);
          assert(p != visited.end());
          visited.erase(p);
      }
   private:
      rvalue_from_python_chain const* chain;
  };
}


BOOST_PYTHON_DECL bool implicit_rvalue_convertible_from_python(
    PyObject* source
    , registration const& converters)
{    
    if (objects::find_instance_impl(source, converters.target_type))
        return true;
    
    rvalue_from_python_chain const* chain = converters.rvalue_chain;
    
    if (!visit(chain))
        return false;

    unvisit protect(chain);
    
    for (;chain != 0; chain = chain->next)
    {
        if (chain->convertible(source))
            return true;
    }

    return false;
}

namespace
{
  void throw_no_lvalue_from_python(PyObject* source, registration const& converters, char const* ref_type)
  {
      handle<> msg(
          ::PyString_FromFormat(
              "No registered converter was able to extract a C++ %s to type %s"
              " from this Python object of type %s"
              , ref_type
              , converters.target_type.name()
              , source->ob_type->tp_name
              ));
              
      PyErr_SetObject(PyExc_TypeError, msg.get());

      throw_error_already_set();
  }

  void* lvalue_result_from_python(
      PyObject* source
      , registration const& converters
      , char const* ref_type)
  {
      handle<> holder(source);
      if (source->ob_refcnt <= 1)
      {
          handle<> msg(
              ::PyString_FromFormat(
                  "Attempt to return dangling %s to object of type: %s"
                  , ref_type
                  , converters.target_type.name()));
          
          PyErr_SetObject(PyExc_ReferenceError, msg.get());

          throw_error_already_set();
      }
      
      void* result = get_lvalue_from_python(source, converters);
      if (!result)
          (throw_no_lvalue_from_python)(source, converters, ref_type);
      return result;
  }
  
}

BOOST_PYTHON_DECL void throw_no_pointer_from_python(PyObject* source, registration const& converters)
{
    (throw_no_lvalue_from_python)(source, converters, "pointer");
}

BOOST_PYTHON_DECL void throw_no_reference_from_python(PyObject* source, registration const& converters)
{
    (throw_no_lvalue_from_python)(source, converters, "reference");
}

BOOST_PYTHON_DECL void* reference_result_from_python(
    PyObject* source
    , registration const& converters)
{
    return (lvalue_result_from_python)(source, converters, "reference");
}
  
BOOST_PYTHON_DECL void* pointer_result_from_python(
    PyObject* source
    , registration const& converters)
{
    if (source == Py_None)
    {
        Py_DECREF(source);
        return 0;
    }
    return (lvalue_result_from_python)(source, converters, "pointer");
}
  
BOOST_PYTHON_DECL void void_result_from_python(PyObject* o)
{
    Py_DECREF(expect_non_null(o));
}

} // namespace boost::python::converter

BOOST_PYTHON_DECL PyObject*
pytype_check(PyTypeObject* type_, PyObject* source)
{
    if (!PyObject_IsInstance(source, python::upcast<PyObject>(type_)))
    {
        ::PyErr_Format(
            PyExc_TypeError
            , "Expecting an object of type %s; got an object of type %s instead"
            , type_->tp_name
            , source->ob_type->tp_name
            );
        throw_error_already_set();
    }
    return source;
}

}} // namespace boost::python