code: def _check_callback(callback, fargs, what="Callback functions"):
      '''Bokeh-internal function to check callback signature'''
      sig = signature(callback)
      formatted_args = format_signature(sig)
      error_msg = what + " must have signature func(%s), got func%s"
  
      all_names, default_values = get_param_info(sig)
  
      nargs = len(all_names) - len(default_values)
      if nargs != len(fargs):
          raise ValueError(error_msg % (", ".join(fargs), formatted_args)f _check_callback(callback, fargs, what="Callback functions"):
      '''Bokeh-internal function to check callback signature'''
      sig = signature(callback)
      formatted_args = format_signature(sig)
      error_msg = what + " must have signature func(%s), got func%s"
  
      all_names, default_values = get_param_info(sig)
  
      nargs = len(all_names) - len(default_values)
      if nargs != len(fargs):
          raise ValueError(error_msg % (", ".join(fargs), formatted_args))
docs: Bokeh-internal function to check callback signature