text: from functools import lru_cache
  
  
  class FunctionDispatch(object):
      """
      FunctionDispatch is similar to functools.singledispatch, but
      instead dispatches based on functions that take the type of the
      first argument in the method, and return True or False.
  
      objects that help determine dispatch should be instantiated objects.
      """
  
      __slots__ = ("_handler_pairs", "dispatch")
  
      def __init__(self):
          self._handler_pairs = []
          self.dispatch = lru_cache(64)(self._dispatch)
  
      def register(self, can_handle, func):
          self._handler_pairs.insert(0, (can_handle, func))
          self.dispatch.cache_clear()
  
      def _dispatch(self, typ):
          """
          returns the appropriate handler, for the object passed.
          """
          for can_handle, handler in self._handler_pairs:
              # can handle could raise an exception here
              # such as issubclass being called on an instance.
              # it's easier to just ignore that case.
              try:
                  if can_handle(typ):
                      return handler
              except Exception:
                  pass
          raise KeyError("unable to find handler for {0}".format(typ))
  