src/transformers/models/mpnet/modeling_mpnet.py/MPNetEncoder/__init__
class MPNetEncoder:    def __init__(self, config):
        super().__init__()
        self.config = config
        self.n_heads = config.num_attention_heads
        self.layer = nn.ModuleList([MPNetLayer(config) for _ in range(config.num_hidden_layers)])
        self.relative_attention_bias = nn.Embedding(config.relative_attention_num_buckets, self.n_heads)