src/transformers/models/xlm/modeling_xlm.py/MultiHeadAttention/__init__
class MultiHeadAttention:    def __init__(self, n_heads, dim, config):
        super().__init__()
        self.layer_id = next(MultiHeadAttention.NEW_ID)
        self.dim = dim
        self.n_heads = n_heads
        self.dropout = config.attention_dropout
        assert self.dim % self.n_heads == 0

        self.q_lin = nn.Linear(dim, dim)
        self.k_lin = nn.Linear(dim, dim)
        self.v_lin = nn.Linear(dim, dim)
        self.out_lin = nn.Linear(dim, dim)
        self.pruned_heads = set()