docs: def activate(self, *, filter_func=None):
          '''
          Activate the type safety checker. After the call all functions
          that need to be checked will be.
          '''
  
          if self.active:
              raise RuntimeError("Type safety check already active")
  
          self.__module_finder = ModuleFinder(Validator.decorate)
          if filter_func is not None:
              self.__module_finder.set_filter(filter_func)
          self.__module_finder.install()