partial class Examples
{
  public static Result InstanceDefinitionNames(RhinoDoc doc)
  {
    var instance-definition-names = (from instance_definition in doc.InstanceDefinitions
                                     where instance_definition != null && !instance_definition.IsDeleted
                                     select instance_definition.Name);

    foreach (var n in instance-definition-names)
      RhinoApp.WriteLine("Instance definition = {0}", n);

    return Result.Success;
  }
}

from scriptcontext import doc

def RunCommand():
    instanceDefinitionNames = [instanceDefinition.Name for instanceDefinition in doc.InstanceDefinitions if instanceDefinition != None and not instanceDefinition.IsDeleted]

    for n in instanceDefinitionNames:
        print("instance definition = {0}".format(n))

if __name__ == "__main__":
    RunCommand()