Add is_writable() method to PropertyMap

This also includes convenience property map checks.

src/graph/graph_python_interface.hh

@@ -459,6 +459,13 @@ public:
         return python::object();
     }
 
+    bool IsWritable() const
+    {
+        return is_convertible<
+            typename property_traits<PropertyMap>::category,
+            readable_property_map_tag>::value;
+    }
+
 private:
     PropertyMap _pmap; // hold an internal copy, since it's cheap
 };

src/graph/graph_python_interface_export.cc

@@ -67,7 +67,8 @@ struct export_vertex_property_map
             .def("__setitem__", &pmap_t::template SetValue<PythonVertex>)
             .def("get_map", &pmap_t::GetMap)
             .def("get_dynamic_map", &pmap_t::GetDynamicMap)
-            .def("get_array", &pmap_t::GetArray);
+            .def("get_array", &pmap_t::GetArray)
+            .def("is_writable", &pmap_t::IsWritable);
     }
 
     string _name;
@@ -132,7 +133,8 @@ struct export_edge_property_map
             .def("value_type", &pmap_t::GetType)
             .def("get_map", &pmap_t::GetMap)
             .def("get_dynamic_map", &pmap_t::GetDynamicMap)
-            .def("get_array", &pmap_t::GetArray);
+            .def("get_array", &pmap_t::GetArray)
+            .def("is_writable", &pmap_t::IsWritable);
 
 
         typedef mpl::transform<graph_tool::detail::all_graph_views,
@@ -175,7 +177,8 @@ struct export_graph_property_map
             .def("__setitem__", &pmap_t::template SetValue<GraphInterface>)
             .def("get_map", &pmap_t::GetMap)
             .def("get_dynamic_map", &pmap_t::GetDynamicMap)
-            .def("get_array", &pmap_t::GetArray);
+            .def("get_array", &pmap_t::GetArray)
+            .def("is_writable", &pmap_t::IsWritable);
     }
 
     string _name;

src/graph_tool/core.py

@@ -201,6 +201,21 @@ class PropertyMap(object):
             n = 1
         return self.__map.get_array(n)
 
+    def is_writable(self):
+        """Return True if the property is writable."""
+        return self.__map.is_writable()
+
+def _check_prop_writable(prop, name=None):
+    if not prop.is_writable():
+        raise ValueError("property map%s is not writable." %\
+                         ((" '%s'" % name) if name != None else ""))
+
+def _check_prop_scalar(prop, name=None):
+    if prop.value_type() not in ["bool", "int32_t", "int64_t", "unsigned long",
+                                 "double", "long double"]:
+        raise ValueError("property map%s is not of scalar type." %\
+                         ((" '%s'" % name) if name != None else ""))
+
 class PropertyDict(dict):
     """Wrapper for the dict of vertex, graph or edge properties, which sets the
     value on the property map when changed in the dict."""