python bindings: export Query.resolution property as a tuple

Although the mapnik::query class is exposed to the Python bindings, the
resolution attribute is a raw boost::tuple. If you attempt to access
this tuple from Python, boost complains strongly.

This patch adds the required magic to marshal the raw boost::tuple which
is query::resolution_type into an honest-to-goodness Python tuple.

bindings/python/mapnik_query.cpp

@@ -30,6 +30,8 @@
 using mapnik::query;
 using mapnik::box2d;
 
+namespace python = boost::python;
+
 struct query_pickle_suite : boost::python::pickle_suite
 {
     static boost::python::tuple
@@ -39,10 +41,26 @@ struct query_pickle_suite : boost::python::pickle_suite
     }
 };
 
+struct resolution_to_tuple
+{
+    static PyObject* convert(query::resolution_type const& x)
+    {
+        python::object tuple(python::make_tuple(x.get<0>(), x.get<1>()));
+        return python::incref(tuple.ptr());
+    }
+
+    static PyTypeObject const* get_pytype()
+    {
+        return &PyTuple_Type;
+    }
+};
+
 void export_query()
 {
     using namespace boost::python;
 
+    to_python_converter<query::resolution_type, resolution_to_tuple> ();
+
     class_<query>("Query", "a spatial query data object",
                   init<box2d<double>,query::resolution_type const&,double>() )
         .def(init<box2d<double> >())

tests/python_tests/query_test.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+import os, mapnik
+
+from nose.tools import *
+from utilities import execution_path
+
+def setup():
+    # All of the paths used are relative, if we run the tests
+    # from another directory we need to chdir()
+    os.chdir(execution_path('.'))
+
+def test_query_init():
+    bbox = (-180, -90, 180, 90)
+    query = mapnik.Query(mapnik.Box2d(*bbox))
+    r = query.resolution
+    assert_almost_equal(r[0], 1.0, places=7)
+    assert_almost_equal(r[1], 1.0, places=7)
+
+# Converting *from* tuples *to* resolutions is not yet supported
+@raises(TypeError)
+def test_query_resolution():
+    bbox = (-180, -90, 180, 90)
+    init_res = (4.5, 6.7)
+    query = mapnik.Query(mapnik.Box2d(*bbox), init_res)
+    r = query.resolution
+    assert_almost_equal(r[0], init_res[0], places=7)
+    assert_almost_equal(r[1], init_res[1], places=7)
+
+if __name__ == "__main__":
+    setup()
+    [eval(run)() for run in dir() if 'test_' in run]