Added is_directed member function

[SVN r27651]

src/python/basic_graph.cpp

@@ -493,6 +493,7 @@ void export_basic_graph(const char* name)
       class_<basic_graph<DirectedS> >(name)
         // Constructors
         .def(init<std::string, graph_file_kind>())
+        .def("is_directed", &Graph::is_directed)
         // Vertex List Graph concept
         .def("num_vertices", &Graph::num_vertices)
         .add_property("vertices", range(&Graph::vertices_begin, 

src/python/basic_graph.hpp

@@ -209,7 +209,10 @@ class basic_graph
 
   basic_graph();
   basic_graph(const std::string& filename, graph_file_kind kind); 
-  
+
+  bool is_directed() const
+  { return is_convertible<directed_category, directed_tag>::value; }
+
   Vertex add_vertex();
   void clear_vertex(Vertex vertex);
   void remove_vertex(Vertex vertex);