text: from ..builder import BBOX_SAMPLERS, build_sampler
  from .base_sampler import BaseSampler
  
  
  @BBOX_SAMPLERS.register_module()
  class CombinedSampler(BaseSampler):
      """A sampler that combines positive sampler and negative sampler."""
  
      def __init__(self, pos_sampler, neg_sampler, **kwargs):
          super(CombinedSampler, self).__init__(**kwargs)
          self.pos_sampler = build_sampler(pos_sampler, **kwargs)
          self.neg_sampler = build_sampler(neg_sampler, **kwargs)
  
      def _sample_pos(self, **kwargs):
          """Sample positive samples."""
          raise NotImplementedError
  
      def _sample_neg(self, **kwargs):
          """Sample negative samples."""
          raise NotImplementedError
  