从去年的ViT以来，Transformer在CV领域也大红大紫，现在写都算比较迟了，这次主要从PyTorch源码角度来看Transformer整体结构。
主要的源码文件位于下面这个路径：
anaconda3/lib/python3.7/site-packages/torch/nn/modules/transformer.py
官方的Transformer文档也可以去这里参考
主要是有一个Transformer类，而这个类也主要由TransformerEncoder和TransformerDecoder组成
Transformer
├── TransformerEncoder
│ ├── TransformerEncoderLayer1
│ ├── TransformerEncoderLayer2
│ ├── ...
├── TransformerDecoder
│ ├── TransformerDecoderLayer1
│ ├── TransformerDecoderLayer2
│ ├── ...
这里先放一张论文“Attention Is All You Need”中的标准Transformer的示意图：
左边的部分就是编码器(encoder)，右边的部分就是解码器(decoder)，具体的连接也可以根据具体任务而进行一些实现上的调整
下面这个Transformer的内容很简单，如果先不去细看编码器和解码器的具体实现，先认为有这个准备着，其实就主要的有两块地方：
-
根据输入参数构造encoder和decoder：主要有d_model输入的特征数，nhead多头注意力的头数，dim_feedforward为FFN的特征数，dropout概率，activation激活函数。归一化统一是Layer Normalization，还有一个就是num_encoder_layers编码器的层数，num_decoder_layers解码器的层数，也就是上面图中的N x，是可以重复很多次的。
# 构造encoder encoder_layer = TransformerEncoderLayer(d_model, nhead, dim_feedforward, dropout, activation) encoder_norm = LayerNorm(d_model) self.encoder = TransformerEncoder(encoder_layer, num_encoder_layers, encoder_norm) # 构造decoder decoder_layer = TransformerDecoderLayer(d_model, nhead, dim_feedforward, dropout, activation) decoder_norm = LayerNorm(d_model) self.decoder = TransformerDecoder(decoder_layer, num_decoder_layers, decoder_norm) -
剩下的就是前向传播了，forward函数里面就是把encoder和decoder过了一下，后面的一些mask可以先不用管，一般也用不到，只要知道encoder的输入是src，decoder的输入是encoder的输出memory和自己的输入tgt：
memory = self.encoder(src, mask=src_mask, src_key_padding_mask=src_key_padding_mask) output = self.decoder(tgt, memory, tgt_mask=tgt_mask, memory_mask=memory_mask, tgt_key_padding_mask=tgt_key_padding_mask, memory_key_padding_mask=memory_key_padding_mask)
其次需要注意一下的就是输入的src的形状了，注释里是这样说的src: :math:(S, N, E)，其中S是源序列的长度。N是batch size大小, E是特征数量。所以这是一个3-D的tensor，一般cv里面的输入都是(B,C,H,W)的4-D的volume，所以一般会经过一个reshape然后再作为encoder的输入: (B,C,H,W)-reshape->(B,C,WH)-pemute->(WH,B,C)，也就是把W*H看成是序列长度，而通道数就看成特征数量。
class Transformer(Module):
r"""A transformer model. User is able to modify the attributes as needed. The architecture
is based on the paper "Attention Is All You Need". Ashish Vaswani, Noam Shazeer,
Niki Parmar, Jakob Uszkoreit, Llion Jones, Aidan N Gomez, Lukasz Kaiser, and
Illia Polosukhin. 2017. Attention is all you need. In Advances in Neural Information
Processing Systems, pages 6000-6010. Users can build the BERT(https://arxiv.org/abs/1810.04805)
model with corresponding parameters.
Args:
d_model: the number of expected features in the encoder/decoder inputs (default=512).
nhead: the number of heads in the multiheadattention models (default=8).
num_encoder_layers: the number of sub-encoder-layers in the encoder (default=6).
num_decoder_layers: the number of sub-decoder-layers in the decoder (default=6).
dim_feedforward: the dimension of the feedforward network model (default=2048).
dropout: the dropout value (default=0.1).
activation: the activation function of encoder/decoder intermediate layer, relu or gelu (default=relu).
custom_encoder: custom encoder (default=None).
custom_decoder: custom decoder (default=None).
Examples::
>>> transformer_model = nn.Transformer(nhead=16, num_encoder_layers=12)
>>> src = torch.rand((10, 32, 512))
>>> tgt = torch.rand((20, 32, 512))
>>> out = transformer_model(src, tgt)
Note: A full example to apply nn.Transformer module for the word language model is available in
https://github.com/pytorch/examples/tree/master/word_language_model
"""
def __init__(self, d_model=512, nhead=8, num_encoder_layers=6,
num_decoder_layers=6, dim_feedforward=2048, dropout=0.1,
activation="relu", custom_encoder=None, custom_decoder=None):
super(Transformer, self).__init__()
if custom_encoder is not None:
self.encoder = custom_encoder
else:
encoder_layer = TransformerEncoderLayer(d_model, nhead, dim_feedforward, dropout, activation)
encoder_norm = LayerNorm(d_model)
self.encoder = TransformerEncoder(encoder_layer, num_encoder_layers, encoder_norm)
if custom_decoder is not None:
self.decoder = custom_decoder
else:
decoder_layer = TransformerDecoderLayer(d_model, nhead, dim_feedforward, dropout, activation)
decoder_norm = LayerNorm(d_model)
self.decoder = TransformerDecoder(decoder_layer, num_decoder_layers, decoder_norm)
self._reset_parameters()
self.d_model = d_model
self.nhead = nhead
def forward(self, src, tgt, src_mask=None, tgt_mask=None,
memory_mask=None, src_key_padding_mask=None,
tgt_key_padding_mask=None, memory_key_padding_mask=None):
r"""Take in and process masked source/target sequences.
Args:
src: the sequence to the encoder (required).
tgt: the sequence to the decoder (required).
src_mask: the additive mask for the src sequence (optional).
tgt_mask: the additive mask for the tgt sequence (optional).
memory_mask: the additive mask for the encoder output (optional).
src_key_padding_mask: the ByteTensor mask for src keys per batch (optional).
tgt_key_padding_mask: the ByteTensor mask for tgt keys per batch (optional).
memory_key_padding_mask: the ByteTensor mask for memory keys per batch (optional).
Shape:
- src: :math:`(S, N, E)`.
- tgt: :math:`(T, N, E)`.
- src_mask: :math:`(S, S)`.
- tgt_mask: :math:`(T, T)`.
- memory_mask: :math:`(T, S)`.
- src_key_padding_mask: :math:`(N, S)`.
- tgt_key_padding_mask: :math:`(N, T)`.
- memory_key_padding_mask: :math:`(N, S)`.
Note: [src/tgt/memory]_mask should be filled with
float('-inf') for the masked positions and float(0.0) else. These masks
ensure that predictions for position i depend only on the unmasked positions
j and are applied identically for each sequence in a batch.
[src/tgt/memory]_key_padding_mask should be a ByteTensor where True values are positions
that should be masked with float('-inf') and False values will be unchanged.
This mask ensures that no information will be taken from position i if
it is masked, and has a separate mask for each sequence in a batch.
- output: :math:`(T, N, E)`.
Note: Due to the multi-head attention architecture in the transformer model,
the output sequence length of a transformer is same as the input sequence
(i.e. target) length of the decode.
where S is the source sequence length, T is the target sequence length, N is the
batch size, E is the feature number
Examples:
>>> output = transformer_model(src, tgt, src_mask=src_mask, tgt_mask=tgt_mask)
"""
if src.size(1) != tgt.size(1):
raise RuntimeError("the batch number of src and tgt must be equal")
if src.size(2) != self.d_model or tgt.size(2) != self.d_model:
raise RuntimeError("the feature number of src and tgt must be equal to d_model")
memory = self.encoder(src, mask=src_mask, src_key_padding_mask=src_key_padding_mask)
output = self.decoder(tgt, memory, tgt_mask=tgt_mask, memory_mask=memory_mask,
tgt_key_padding_mask=tgt_key_padding_mask,
memory_key_padding_mask=memory_key_padding_mask)
return output
def generate_square_subsequent_mask(self, sz):
r"""Generate a square mask for the sequence. The masked positions are filled with float('-inf').
Unmasked positions are filled with float(0.0).
"""
mask = (torch.triu(torch.ones(sz, sz)) == 1).transpose(0, 1)
mask = mask.float().masked_fill(mask == 0, float('-inf')).masked_fill(mask == 1, float(0.0))
return mask
def _reset_parameters(self):
r"""Initiate parameters in the transformer model."""
for p in self.parameters():
if p.dim() > 1:
xavier_uniform_(p)
下面就从encoder和decoder部分看看是怎么实现的，其实也没有很多展开来，最主要的的是一个MultiheadAttention：
编码器部分，主要有TransformerEncoder和TransformerEncoderLayer类：
- TransformerEncoder：基本上没什么好讲的，就是依次通过num_layers层的TransformerEncoderLayer
- TransformerEncoderLayer：主要就是实现了上面标准的Transformer的左半部分，其中可能有些dropout和激活函数是图中没有画出来的，对照着示意图很容易看
class TransformerEncoder(Module):
r"""TransformerEncoder is a stack of N encoder layers
Args:
encoder_layer: an instance of the TransformerEncoderLayer() class (required).
num_layers: the number of sub-encoder-layers in the encoder (required).
norm: the layer normalization component (optional).
Examples::
>>> encoder_layer = nn.TransformerEncoderLayer(d_model=512, nhead=8)
>>> transformer_encoder = nn.TransformerEncoder(encoder_layer, num_layers=6)
>>> src = torch.rand(10, 32, 512)
>>> out = transformer_encoder(src)
"""
def __init__(self, encoder_layer, num_layers, norm=None):
super(TransformerEncoder, self).__init__()
self.layers = _get_clones(encoder_layer, num_layers)
self.num_layers = num_layers
self.norm = norm
def forward(self, src, mask=None, src_key_padding_mask=None):
r"""Pass the input through the encoder layers in turn.
Args:
src: the sequnce to the encoder (required).
mask: the mask for the src sequence (optional).
src_key_padding_mask: the mask for the src keys per batch (optional).
Shape:
see the docs in Transformer class.
"""
output = src
for i in range(self.num_layers):
output = self.layers[i](output, src_mask=mask,
src_key_padding_mask=src_key_padding_mask)
if self.norm:
output = self.norm(output)
return output
class TransformerEncoderLayer(Module):
r"""TransformerEncoderLayer is made up of self-attn and feedforward network.
This standard encoder layer is based on the paper "Attention Is All You Need".
Ashish Vaswani, Noam Shazeer, Niki Parmar, Jakob Uszkoreit, Llion Jones, Aidan N Gomez,
Lukasz Kaiser, and Illia Polosukhin. 2017. Attention is all you need. In Advances in
Neural Information Processing Systems, pages 6000-6010. Users may modify or implement
in a different way during application.
Args:
d_model: the number of expected features in the input (required).
nhead: the number of heads in the multiheadattention models (required).
dim_feedforward: the dimension of the feedforward network model (default=2048).
dropout: the dropout value (default=0.1).
activation: the activation function of intermediate layer, relu or gelu (default=relu).
Examples::
>>> encoder_layer = nn.TransformerEncoderLayer(d_model=512, nhead=8)
>>> src = torch.rand(10, 32, 512)
>>> out = encoder_layer(src)
"""
def __init__(self, d_model, nhead, dim_feedforward=2048, dropout=0.1, activation="relu"):
super(TransformerEncoderLayer, self).__init__()
self.self_attn = MultiheadAttention(d_model, nhead, dropout=dropout)
# Implementation of Feedforward model
self.linear1 = Linear(d_model, dim_feedforward)
self.dropout = Dropout(dropout)
self.linear2 = Linear(dim_feedforward, d_model)
self.norm1 = LayerNorm(d_model)
self.norm2 = LayerNorm(d_model)
self.dropout1 = Dropout(dropout)
self.dropout2 = Dropout(dropout)
self.activation = _get_activation_fn(activation)
def forward(self, src, src_mask=None, src_key_padding_mask=None):
r"""Pass the input through the encoder layer.
Args:
src: the sequnce to the encoder layer (required).
src_mask: the mask for the src sequence (optional).
src_key_padding_mask: the mask for the src keys per batch (optional).
Shape:
see the docs in Transformer class.
"""
src2 = self.self_attn(src, src, src, attn_mask=src_mask,
key_padding_mask=src_key_padding_mask)[0]
src = src + self.dropout1(src2)
src = self.norm1(src)
if hasattr(self, "activation"):
src2 = self.linear2(self.dropout(self.activation(self.linear1(src))))
else: # for backward compatibility
src2 = self.linear2(self.dropout(F.relu(self.linear1(src))))
src = src + self.dropout2(src2)
src = self.norm2(src)
return src
解码器部分，主要有TransformerDecoder和TransformerDecoderLayer类：
- TransformerDecoder：基本上没什么好讲的，就是依次通过num_layers层的TransformerDecoderLayer
- TransformerDecoderLayer：主要就是实现了上面标准的Transformer的右半部分，其中可能有些dropout和激活函数是图中没有画出来的，对照着示意图很容易看，比encoder多了一个MultiheadAttention，其中一个就作为self-attention，另一个是从encoder过来的cross-attention。
class TransformerDecoder(Module):
r"""TransformerDecoder is a stack of N decoder layers
Args:
decoder_layer: an instance of the TransformerDecoderLayer() class (required).
num_layers: the number of sub-decoder-layers in the decoder (required).
norm: the layer normalization component (optional).
Examples::
>>> decoder_layer = nn.TransformerDecoderLayer(d_model=512, nhead=8)
>>> transformer_decoder = nn.TransformerDecoder(decoder_layer, num_layers=6)
>>> memory = torch.rand(10, 32, 512)
>>> tgt = torch.rand(20, 32, 512)
>>> out = transformer_decoder(tgt, memory)
"""
def __init__(self, decoder_layer, num_layers, norm=None):
super(TransformerDecoder, self).__init__()
self.layers = _get_clones(decoder_layer, num_layers)
self.num_layers = num_layers
self.norm = norm
def forward(self, tgt, memory, tgt_mask=None,
memory_mask=None, tgt_key_padding_mask=None,
memory_key_padding_mask=None):
r"""Pass the inputs (and mask) through the decoder layer in turn.
Args:
tgt: the sequence to the decoder (required).
memory: the sequnce from the last layer of the encoder (required).
tgt_mask: the mask for the tgt sequence (optional).
memory_mask: the mask for the memory sequence (optional).
tgt_key_padding_mask: the mask for the tgt keys per batch (optional).
memory_key_padding_mask: the mask for the memory keys per batch (optional).
Shape:
see the docs in Transformer class.
"""
output = tgt
for i in range(self.num_layers):
output = self.layers[i](output, memory, tgt_mask=tgt_mask,
memory_mask=memory_mask,
tgt_key_padding_mask=tgt_key_padding_mask,
memory_key_padding_mask=memory_key_padding_mask)
if self.norm:
output = self.norm(output)
return output
class TransformerDecoderLayer(Module):
r"""TransformerDecoderLayer is made up of self-attn, multi-head-attn and feedforward network.
This standard decoder layer is based on the paper "Attention Is All You Need".
Ashish Vaswani, Noam Shazeer, Niki Parmar, Jakob Uszkoreit, Llion Jones, Aidan N Gomez,
Lukasz Kaiser, and Illia Polosukhin. 2017. Attention is all you need. In Advances in
Neural Information Processing Systems, pages 6000-6010. Users may modify or implement
in a different way during application.
Args:
d_model: the number of expected features in the input (required).
nhead: the number of heads in the multiheadattention models (required).
dim_feedforward: the dimension of the feedforward network model (default=2048).
dropout: the dropout value (default=0.1).
activation: the activation function of intermediate layer, relu or gelu (default=relu).
Examples::
>>> decoder_layer = nn.TransformerDecoderLayer(d_model=512, nhead=8)
>>> memory = torch.rand(10, 32, 512)
>>> tgt = torch.rand(20, 32, 512)
>>> out = decoder_layer(tgt, memory)
"""
def __init__(self, d_model, nhead, dim_feedforward=2048, dropout=0.1, activation="relu"):
super(TransformerDecoderLayer, self).__init__()
self.self_attn = MultiheadAttention(d_model, nhead, dropout=dropout)
self.multihead_attn = MultiheadAttention(d_model, nhead, dropout=dropout)
# Implementation of Feedforward model
self.linear1 = Linear(d_model, dim_feedforward)
self.dropout = Dropout(dropout)
self.linear2 = Linear(dim_feedforward, d_model)
self.norm1 = LayerNorm(d_model)
self.norm2 = LayerNorm(d_model)
self.norm3 = LayerNorm(d_model)
self.dropout1 = Dropout(dropout)
self.dropout2 = Dropout(dropout)
self.dropout3 = Dropout(dropout)
self.activation = _get_activation_fn(activation)
def forward(self, tgt, memory, tgt_mask=None, memory_mask=None,
tgt_key_padding_mask=None, memory_key_padding_mask=None):
r"""Pass the inputs (and mask) through the decoder layer.
Args:
tgt: the sequence to the decoder layer (required).
memory: the sequnce from the last layer of the encoder (required).
tgt_mask: the mask for the tgt sequence (optional).
memory_mask: the mask for the memory sequence (optional).
tgt_key_padding_mask: the mask for the tgt keys per batch (optional).
memory_key_padding_mask: the mask for the memory keys per batch (optional).
Shape:
see the docs in Transformer class.
"""
tgt2 = self.self_attn(tgt, tgt, tgt, attn_mask=tgt_mask,
key_padding_mask=tgt_key_padding_mask)[0]
tgt = tgt + self.dropout1(tgt2)
tgt = self.norm1(tgt)
tgt2 = self.multihead_attn(tgt, memory, memory, attn_mask=memory_mask,
key_padding_mask=memory_key_padding_mask)[0]
tgt = tgt + self.dropout2(tgt2)
tgt = self.norm2(tgt)
if hasattr(self, "activation"):
tgt2 = self.linear2(self.dropout(self.activation(self.linear1(tgt))))
else: # for backward compatibility
tgt2 = self.linear2(self.dropout(F.relu(self.linear1(tgt))))
tgt = tgt + self.dropout3(tgt2)
tgt = self.norm3(tgt)
return tgt
def _get_clones(module, N):
return ModuleList([copy.deepcopy(module) for i in range(N)])
def _get_activation_fn(activation):
if activation == "relu":
return F.relu
elif activation == "gelu":
return F.gelu
else:
raise RuntimeError("activation should be relu/gelu, not %s." % activation)
这里也放一下MultiHeadAttention的源码吧，不过具体实现F.multi_head_attention_forward也是看不到的，具体原理可以看我最后放的李宏毅老师的讲解视频。
class MultiheadAttention(Module):
r"""Allows the model to jointly attend to information
from different representation subspaces.
See reference: Attention Is All You Need
.. math::
\text{MultiHead}(Q, K, V) = \text{Concat}(head_1,\dots,head_h)W^O
\text{where} head_i = \text{Attention}(QW_i^Q, KW_i^K, VW_i^V)
Args:
embed_dim: total dimension of the model.
num_heads: parallel attention heads.
dropout: a Dropout layer on attn_output_weights. Default: 0.0.
bias: add bias as module parameter. Default: True.
add_bias_kv: add bias to the key and value sequences at dim=0.
add_zero_attn: add a new batch of zeros to the key and
value sequences at dim=1.
kdim: total number of features in key. Default: None.
vdim: total number of features in key. Default: None.
Note: if kdim and vdim are None, they will be set to embed_dim such that
query, key, and value have the same number of features.
Examples::
>>> multihead_attn = nn.MultiheadAttention(embed_dim, num_heads)
>>> attn_output, attn_output_weights = multihead_attn(query, key, value)
"""
__annotations__ = {
'bias_k': torch._jit_internal.Optional[torch.Tensor],
'bias_v': torch._jit_internal.Optional[torch.Tensor],
}
__constants__ = ['q_proj_weight', 'k_proj_weight', 'v_proj_weight', 'in_proj_weight']
def __init__(self, embed_dim, num_heads, dropout=0., bias=True, add_bias_kv=False, add_zero_attn=False, kdim=None, vdim=None):
super(MultiheadAttention, self).__init__()
self.embed_dim = embed_dim
self.kdim = kdim if kdim is not None else embed_dim
self.vdim = vdim if vdim is not None else embed_dim
self._qkv_same_embed_dim = self.kdim == embed_dim and self.vdim == embed_dim
self.num_heads = num_heads
self.dropout = dropout
self.head_dim = embed_dim // num_heads
assert self.head_dim * num_heads == self.embed_dim, "embed_dim must be divisible by num_heads"
if self._qkv_same_embed_dim is False:
self.q_proj_weight = Parameter(torch.Tensor(embed_dim, embed_dim))
self.k_proj_weight = Parameter(torch.Tensor(embed_dim, self.kdim))
self.v_proj_weight = Parameter(torch.Tensor(embed_dim, self.vdim))
self.register_parameter('in_proj_weight', None)
else:
self.in_proj_weight = Parameter(torch.empty(3 * embed_dim, embed_dim))
self.register_parameter('q_proj_weight', None)
self.register_parameter('k_proj_weight', None)
self.register_parameter('v_proj_weight', None)
if bias:
self.in_proj_bias = Parameter(torch.empty(3 * embed_dim))
else:
self.register_parameter('in_proj_bias', None)
self.out_proj = Linear(embed_dim, embed_dim, bias=bias)
if add_bias_kv:
self.bias_k = Parameter(torch.empty(1, 1, embed_dim))
self.bias_v = Parameter(torch.empty(1, 1, embed_dim))
else:
self.bias_k = self.bias_v = None
self.add_zero_attn = add_zero_attn
self._reset_parameters()
def _reset_parameters(self):
if self._qkv_same_embed_dim:
xavier_uniform_(self.in_proj_weight)
else:
xavier_uniform_(self.q_proj_weight)
xavier_uniform_(self.k_proj_weight)
xavier_uniform_(self.v_proj_weight)
if self.in_proj_bias is not None:
constant_(self.in_proj_bias, 0.)
constant_(self.out_proj.bias, 0.)
if self.bias_k is not None:
xavier_normal_(self.bias_k)
if self.bias_v is not None:
xavier_normal_(self.bias_v)
def __setstate__(self, state):
super(MultiheadAttention, self).__setstate__(state)
# Support loading old MultiheadAttention checkpoints generated by v1.1.0
if 'self._qkv_same_embed_dim' not in self.__dict__:
self._qkv_same_embed_dim = True
def forward(self, query, key, value, key_padding_mask=None,
need_weights=True, attn_mask=None):
# type: (Tensor, Tensor, Tensor, Optional[Tensor], bool, Optional[Tensor]) -> Tuple[Tensor, Optional[Tensor]]
r"""
Args:
query, key, value: map a query and a set of key-value pairs to an output.
See "Attention Is All You Need" for more details.
key_padding_mask: if provided, specified padding elements in the key will
be ignored by the attention. This is an binary mask. When the value is True,
the corresponding value on the attention layer will be filled with -inf.
need_weights: output attn_output_weights.
attn_mask: mask that prevents attention to certain positions. This is an additive mask
(i.e. the values will be added to the attention layer).
Shape:
- Inputs:
- query: :math:`(L, N, E)` where L is the target sequence length, N is the batch size, E is
the embedding dimension.
- key: :math:`(S, N, E)`, where S is the source sequence length, N is the batch size, E is
the embedding dimension.
- value: :math:`(S, N, E)` where S is the source sequence length, N is the batch size, E is
the embedding dimension.
- key_padding_mask: :math:`(N, S)`, ByteTensor, where N is the batch size, S is the source sequence length.
- attn_mask: :math:`(L, S)` where L is the target sequence length, S is the source sequence length.
- Outputs:
- attn_output: :math:`(L, N, E)` where L is the target sequence length, N is the batch size,
E is the embedding dimension.
- attn_output_weights: :math:`(N, L, S)` where N is the batch size,
L is the target sequence length, S is the source sequence length.
"""
if not self._qkv_same_embed_dim:
return F.multi_head_attention_forward(
query, key, value, self.embed_dim, self.num_heads,
self.in_proj_weight, self.in_proj_bias,
self.bias_k, self.bias_v, self.add_zero_attn,
self.dropout, self.out_proj.weight, self.out_proj.bias,
training=self.training,
key_padding_mask=key_padding_mask, need_weights=need_weights,
attn_mask=attn_mask, use_separate_proj_weight=True,
q_proj_weight=self.q_proj_weight, k_proj_weight=self.k_proj_weight,
v_proj_weight=self.v_proj_weight)
else:
return F.multi_head_attention_forward(
query, key, value, self.embed_dim, self.num_heads,
self.in_proj_weight, self.in_proj_bias,
self.bias_k, self.bias_v, self.add_zero_attn,
self.dropout, self.out_proj.weight, self.out_proj.bias,
training=self.training,
key_padding_mask=key_padding_mask, need_weights=need_weights,
attn_mask=attn_mask)
其实这样一看也没啥神秘的，大家用的时候就是考虑哪些作为query, key, value以及各种连接的方式而已，对于其他的都也是直接调用的，不过这种attention的方式确实在很多CV任务里被证实有更强大的特征提取和关注能力，还可以水水论文…
关于Transformer的优质资源
- 李宏毅视频讲解：https://youtu.be/ugWDIIOHtPA 或者 https://www.bilibili.com/video/BV1J441137V6
- 李宏毅讲解slide：http://speech.ee.ntu.edu.tw/~tlkagk/courses/ML_2019/Lecture/Transformer%20(v5).pdf
- The Illustrated Transformer：http://jalammar.github.io/illustrated-transformer/