Transformer-THUCNews/Classification/scripts/model.py

import torch
import torch.nn as nn
import torch.nn.functional as F
import numpy as np
import copy


class Config(object):
    """配置参数"""

    def __init__(self, dataset, embedding):
        self.model_name = "Transformer"
        self.train_path = dataset + "/data/train.txt"  # 训练集
        self.dev_path = dataset + "/data/dev.txt"  # 验证集
        self.test_path = dataset + "/data/test.txt"  # 测试集
        self.class_list = [
            x.strip()
            for x in open(dataset + "/data/class.txt", encoding="utf-8").readlines()
        ]  # 类别名单
        self.vocab_path = dataset + "/data/vocab.pkl"  # 词表
        self.save_path = (
            dataset + "/saved_dict/" + self.model_name + ".ckpt"
        )  # 模型训练结果
        self.log_path = dataset + "/log/" + self.model_name
        self.embedding_pretrained = (
            torch.tensor(
                np.load(dataset + "/data/" + embedding)["embeddings"].astype("float32")
            )
            if embedding != "random"
            else None
        )  # 预训练词向量
        self.device = torch.device(
            "cuda" if torch.cuda.is_available() else "cpu"
        )  # 设备

        self.dropout = 0.5  # 随机失活
        self.require_improvement = 2000  # 若超过1000batch效果还没提升，则提前结束训练
        self.num_classes = len(self.class_list)  # 类别数
        self.n_vocab = 0  # 词表大小，在运行时赋值
        self.num_epochs = 20  # epoch数
        self.batch_size = 128  # mini-batch大小
        self.pad_size = 32  # 每句话处理成的长度(短填长切)
        self.learning_rate = 5e-4  # 学习率
        self.embed = (
            self.embedding_pretrained.size(1)
            if self.embedding_pretrained is not None
            else 300
        )  # 字向量维度
        self.dim_model = 300
        self.hidden = 1024
        self.last_hidden = 512
        self.num_head = 5
        self.num_encoder = 2


"""Attention Is All You Need"""


class Transformer(nn.Module):
    def __init__(self, config):
        super(Transformer, self).__init__()
        if config.embedding_pretrained is not None:
            self.embedding = nn.Embedding.from_pretrained(
                config.embedding_pretrained, freeze=False
            )
        else:
            self.embedding = nn.Embedding(
                config.n_vocab, config.embed, padding_idx=config.n_vocab - 1
            )

        self.postion_embedding = Positional_Encoding(
            config.embed, config.pad_size, config.dropout, config.device
        )
        self.encoder = Encoder(
            config.dim_model, config.num_head, config.hidden, config.dropout
        )
        self.encoders = nn.ModuleList(
            [
                copy.deepcopy(self.encoder)
                # Encoder(config.dim_model, config.num_head, config.hidden, config.dropout)
                for _ in range(config.num_encoder)
            ]
        )

        self.fc1 = nn.Linear(config.pad_size * config.dim_model, config.num_classes)
        # self.fc2 = nn.Linear(config.last_hidden, config.num_classes)
        # self.fc1 = nn.Linear(config.dim_model, config.num_classes)

    def forward(self, x):
        out = self.embedding(x[0])
        out = self.postion_embedding(out)
        for encoder in self.encoders:
            out = encoder(out)
        out = out.view(out.size(0), -1)
        # out = torch.mean(out, 1)
        out = self.fc1(out)
        return out
    
    def feature(self, x):
        """
        提取中间层特征向量，用于可视化
        返回Transformer编码器输出的flatten特征（全连接层前面的那一层）
        """
        with torch.no_grad():
            out = self.embedding(x[0])
            out = self.postion_embedding(out)
            for encoder in self.encoders:
                out = encoder(out)
            features = out.view(out.size(0), -1)  # [batch_size, pad_size * dim_model]
            return features.cpu().numpy()
    
    def get_prediction(self, x):
        """
        获取模型最终层输出向量（logits）
        """
        with torch.no_grad():
            out = self.embedding(x[0])
            out = self.postion_embedding(out)
            for encoder in self.encoders:
                out = encoder(out)
            out = out.view(out.size(0), -1)
            predictions = self.fc1(out)  # [batch_size, num_classes]
            return predictions.cpu().numpy()
    
    def prediction(self, features):
        """
        根据中间特征向量预测结果
        features: 来自feature()函数的输出 [batch_size, pad_size * dim_model]
        """
        with torch.no_grad():
            features_tensor = torch.tensor(features, dtype=torch.float32).to(next(self.parameters()).device)
            predictions = self.fc1(features_tensor)  # 直接通过最后的分类层
            return predictions.cpu().numpy()


class Encoder(nn.Module):
    def __init__(self, dim_model, num_head, hidden, dropout):
        super(Encoder, self).__init__()
        self.attention = Multi_Head_Attention(dim_model, num_head, dropout)
        self.feed_forward = Position_wise_Feed_Forward(dim_model, hidden, dropout)

    def forward(self, x):
        out = self.attention(x)
        out = self.feed_forward(out)
        return out


class Positional_Encoding(nn.Module):
    def __init__(self, embed, pad_size, dropout, device):
        super(Positional_Encoding, self).__init__()
        self.device = device
        self.pe = torch.tensor(
            [
                [pos / (10000.0 ** (i // 2 * 2.0 / embed)) for i in range(embed)]
                for pos in range(pad_size)
            ]
        )
        self.pe[:, 0::2] = np.sin(self.pe[:, 0::2])
        self.pe[:, 1::2] = np.cos(self.pe[:, 1::2])
        self.dropout = nn.Dropout(dropout)

    def forward(self, x):
        out = x + nn.Parameter(self.pe, requires_grad=False).to(self.device)
        out = self.dropout(out)
        return out


class Scaled_Dot_Product_Attention(nn.Module):
    """Scaled Dot-Product Attention"""

    def __init__(self):
        super(Scaled_Dot_Product_Attention, self).__init__()

    def forward(self, Q, K, V, scale=None):
        """
        Args:
            Q: [batch_size, len_Q, dim_Q]
            K: [batch_size, len_K, dim_K]
            V: [batch_size, len_V, dim_V]
            scale: 缩放因子 论文为根号dim_K
        Return:
            self-attention后的张量，以及attention张量
        """
        attention = torch.matmul(Q, K.permute(0, 2, 1))
        if scale:
            attention = attention * scale
        # if mask:  # TODO change this
        #     attention = attention.masked_fill_(mask == 0, -1e9)
        attention = F.softmax(attention, dim=-1)
        context = torch.matmul(attention, V)
        return context


class Multi_Head_Attention(nn.Module):
    def __init__(self, dim_model, num_head, dropout=0.0):
        super(Multi_Head_Attention, self).__init__()
        self.num_head = num_head
        assert dim_model % num_head == 0
        self.dim_head = dim_model // self.num_head
        self.fc_Q = nn.Linear(dim_model, num_head * self.dim_head)
        self.fc_K = nn.Linear(dim_model, num_head * self.dim_head)
        self.fc_V = nn.Linear(dim_model, num_head * self.dim_head)
        self.attention = Scaled_Dot_Product_Attention()
        self.fc = nn.Linear(num_head * self.dim_head, dim_model)
        self.dropout = nn.Dropout(dropout)
        self.layer_norm = nn.LayerNorm(dim_model)

    def forward(self, x):
        batch_size = x.size(0)
        Q = self.fc_Q(x)
        K = self.fc_K(x)
        V = self.fc_V(x)
        Q = Q.view(batch_size * self.num_head, -1, self.dim_head)
        K = K.view(batch_size * self.num_head, -1, self.dim_head)
        V = V.view(batch_size * self.num_head, -1, self.dim_head)
        # if mask:  # TODO
        #     mask = mask.repeat(self.num_head, 1, 1)  # TODO change this
        scale = K.size(-1) ** -0.5  # 缩放因子
        context = self.attention(Q, K, V, scale)

        context = context.view(batch_size, -1, self.dim_head * self.num_head)
        out = self.fc(context)
        out = self.dropout(out)
        out = out + x  # 残差连接
        out = self.layer_norm(out)
        return out


class Position_wise_Feed_Forward(nn.Module):
    def __init__(self, dim_model, hidden, dropout=0.0):
        super(Position_wise_Feed_Forward, self).__init__()
        self.fc1 = nn.Linear(dim_model, hidden)
        self.fc2 = nn.Linear(hidden, dim_model)
        self.dropout = nn.Dropout(dropout)
        self.layer_norm = nn.LayerNorm(dim_model)

    def forward(self, x):
        out = self.fc1(x)
        out = F.relu(out)
        out = self.fc2(out)
        out = self.dropout(out)
        out = out + x  # 残差连接
        out = self.layer_norm(out)
        return out