def __init__(self, combine_method, **kwargs):
    """Constructor.

    Args:
      combine_method: String. The method used to combine the input feature maps
        into a single output feature map. One of 'sum', 'weighted_sum',
        'attention', or 'fast_attention'.
      **kwargs: Additional Keras layer arguments.
    """
    super(BiFPNCombineLayer, self).__init__(**kwargs)
    self.combine_method = combine_method
Constructor.

    Args:
      combine_method: String. The method used to combine the input feature maps
        into a single output feature map. One of 'sum', 'weighted_sum',
        'attention', or 'fast_attention'.
      **kwargs: Additional Keras layer arguments.
    
inference_api/src/main/object_detection/utils/bifpn_utils.py