code: def send_msg(self, message_type, payload=None):
      if payload is None:
          payload = {}
      content = {"type": message_type, "payload": payload}
      self.send(content=content, buffers=None)
  
file_path: pythreejs/pythreejs/_base/renderable.py
imports: from ipywidgets import DOMWidget, Widget, widget_serialization
  from traitlets import Unicode, CInt, Enum, Bool, Int, Instance, List
  from .._package import npm_pkg_name
  from .._version import EXTENSION_SPEC_VERSION
  from .Three import ThreeWidget
  from ..enums import ToneMappings
  from ..math.Plane_autogen import Plane
  from ..renderers.webgl.WebGLShadowMap_autogen import WebGLShadowMap
  from ..traits import IEEEFloat
label_desc: Use image node_id 1 for calling the RenderableWidget obj's underlying member method code with example usage: obj.send_msg(message_type, payload) without return types