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