src/transformers/models/bert_generation/modeling_bert_generation.py/BertGenerationAttention/__init__
class BertGenerationAttention:    def __init__(self, config, position_embedding_type=None):
        super().__init__()
        self.self = BertGenerationSelfAttention(config, position_embedding_type=position_embedding_type)
        self.output = BertGenerationSelfOutput(config)
        self.pruned_heads = set()