[feature][GridFunction] Allow to evaluate with only an element assuming

evaluation at local center.

dune/python/grid/function.hh

@@ -149,6 +149,14 @@ namespace Dune
           pybind11::keep_alive< 0, 1 >(),
           pybind11::keep_alive< 0, 2 >() );
 
+      cls.def( "__call__", [] ( const GridFunction &self, const Element &element ) {
+          LocalCoordinate x ( 0.5 );
+          auto lf = localFunction(self);
+          lf.bind(element);
+          auto y = detail::callLocalFunction< LocalCoordinate >( lf, x, PriorityTag<2>() );
+          lf.unbind();
+          return int(y);
+        }, "element"_a );
       cls.def( "__call__", [] ( const GridFunction &self, const Element &element, LocalCoordinate &x ) {
           auto lf = localFunction(self);
           lf.bind(element);