class_docstr: RPN Head
  
  Args:
      anchor_generator (object): `AnchorGenerator` instance
      rpn_target_assign (object): `RPNTargetAssign` instance
      train_proposal (object): `GenerateProposals` instance for training
      test_proposal (object): `GenerateProposals` instance for testing
      num_classes (int): number of classes in rpn output
code: def __init__(
      self,
      anchor_generator,
      rpn_target_assign,
      train_proposal,
      test_proposal,
      num_classes=1,
  ):
      super(RPNHead, self).__init__()
      self.anchor_generator = anchor_generator
      self.rpn_target_assign = rpn_target_assign
      self.train_proposal = train_proposal
      self.test_proposal = test_proposal
      self.num_classes = num_classes
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from paddle import fluid
  from paddle.fluid.param_attr import ParamAttr
  from paddle.fluid.initializer import Normal
  from paddle.fluid.regularizer import L2Decay
label_desc: Use image node_id 1 to create a new RPNHead object from inherited base classes: object with example: obj = RPNHead(anchor_generator, rpn_target_assign, train_proposal, test_proposal, num_classes)