def add_extra_model_fields(sender, **kwargs):
 model_key = (sender._meta.app_label, sender._meta.model_name)
 for (field_name, field) in fields.get(model_key, {}):
  field.contribute_to_class(sender, field_name)

def add_extra_model_fields ( sender , ** kwargs ) : model_key = ( sender . _meta . app_label , sender . _meta . model_name ) for ( field_name , field ) in fields . get ( model_key , { } ) : field . contribute_to_class ( sender , field_name )
injects custom fields onto the given sender model as defined by the extra_model_fields setting .