code: def is_depsignal_handler(class_, signal_name, cb, *, defer=False):
      
      try:
          handlers = get_magic_attr(cb)
      except AttributeError:
          return False
  
      return _depsignal_spec(class_, signal_name, cb, defer) in handlers
docs: Return true if `cb` has been decorated with :func:`depsignal` for the given
      signal, class and connection mode.