class_docstr: A proxy to access variables defined in a layer. 
docstr: Args:
      kwargs: {name:variable}
docstr_tok: ["Args",":","kwargs",":","{","name",":","variable","}"]
code: def __init__(self, **kwargs):
      """
      Args:
          kwargs: {name:variable}
      """
      self._vars = {}
      for k, v in six.iteritems(kwargs):
          self._add_variable(k, v)
  
imports: import six
label_desc: Use image node_id 1 to create a new VariableHolder object from inherited base classes: object with example: obj = VariableHolder()