FunctionGraph.attach_feature, the method that attaches the feature to the
FunctionGraph. Since this is called after the
FunctionGraphis initially populated, this is where you should run checks on the initial contents of the
The on_attach method may raise the
AlreadyThereexception to cancel the attach operation if it detects that another Feature instance implementing the same functionality is already attached to the
The feature has great freedom in what it can do with the
fgraph: it may, for example, add methods to it dynamically.