fix access to mapnik::query::property_names in python - closes #1762

bindings/python/mapnik_query.cpp

@@ -22,11 +22,15 @@
 
 // boost
 #include <boost/python.hpp>
+#include <boost/foreach.hpp>
 
 // mapnik
 #include <mapnik/query.hpp>
 #include <mapnik/box2d.hpp>
 
+#include <string>
+#include <set>
+
 using mapnik::query;
 using mapnik::box2d;
 
@@ -46,11 +50,30 @@ struct resolution_to_tuple
     }
 };
 
+struct names_to_list
+{
+    static PyObject* convert(std::set<std::string> const& names)
+    {
+        boost::python::list l;
+        BOOST_FOREACH( std::string const& name, names )
+        {
+            l.append(name);
+        }
+        return python::incref(l.ptr());
+    }
+
+    static PyTypeObject const* get_pytype()
+    {
+        return &PyList_Type;
+    }
+};
+
 void export_query()
 {
     using namespace boost::python;
 
     to_python_converter<query::resolution_type, resolution_to_tuple> ();
+    to_python_converter<std::set<std::string>, names_to_list> ();
 
     class_<query>("Query", "a spatial query data object",
                   init<box2d<double>,query::resolution_type const&,double>() )

tests/python_tests/query_test.py

@@ -17,6 +17,10 @@ def test_query_init():
     r = query.resolution
     assert_almost_equal(r[0], 1.0, places=7)
     assert_almost_equal(r[1], 1.0, places=7)
+    # https://github.com/mapnik/mapnik/issues/1762
+    eq_(query.property_names,[])
+    query.add_property_name('migurski')
+    eq_(query.property_names,['migurski'])
 
 # Converting *from* tuples *to* resolutions is not yet supported
 @raises(TypeError)