src/transformers/models/bert/modeling_bert.py/BertAttention/__init__
class BertAttention:    def __init__(self, config, position_embedding_type=None):
        super().__init__()
        self.self = BertSelfAttention(config, position_embedding_type=position_embedding_type)
        self.output = BertSelfOutput(config)
        self.pruned_heads = set()