fastNLP/docs/source/_static/notebooks/tutorial_9_callback.ipynb

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   "source": [
    "# 使用 Callback 自定义你的训练过程"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- 什么是 Callback\n",
    "- 使用 Callback \n",
    "- 一些常用的 Callback\n",
    "- 自定义实现 Callback"
   ]
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   "source": [
    "什么是Callback\n",
    "------\n",
    "\n",
    "Callback 是与 Trainer 紧密结合的模块，利用 Callback 可以在 Trainer 训练时，加入自定义的操作，比如梯度裁剪，学习率调节，测试模型的性能等。定义的 Callback 会在训练的特定阶段被调用。\n",
    "\n",
    "fastNLP 中提供了很多常用的 Callback ，开箱即用。"
   ]
  },
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   "source": [
    "使用 Callback\n",
    " ------\n",
    "\n",
    "使用 Callback 很简单，将需要的 callback 按 list 存储，以对应参数 ``callbacks`` 传入对应的 Trainer。Trainer 在训练时就会自动执行这些 Callback 指定的操作了。"
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     "text": [
      "In total 3 datasets:\n",
      "\ttest has 1200 instances.\n",
      "\ttrain has 9600 instances.\n",
      "\tdev has 1200 instances.\n",
      "In total 2 vocabs:\n",
      "\tchars has 4409 entries.\n",
      "\ttarget has 2 entries.\n",
      "\n",
      "training epochs started 2019-09-17-03-34-34\n"
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     "text": [
      "Evaluate data in 0.1 seconds!\n",
      "Evaluation on dev at Epoch 1/3. Step:300/900: \n",
      "AccuracyMetric: acc=0.863333\n",
      "\n"
     ]
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     "text": [
      "Evaluate data in 0.11 seconds!\n",
      "Evaluation on dev at Epoch 2/3. Step:600/900: \n",
      "AccuracyMetric: acc=0.886667\n",
      "\n"
     ]
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     "text": [
      "Evaluate data in 0.1 seconds!\n",
      "Evaluation on dev at Epoch 3/3. Step:900/900: \n",
      "AccuracyMetric: acc=0.890833\n",
      "\n",
      "\r\n",
      "In Epoch:3/Step:900, got best dev performance:\n",
      "AccuracyMetric: acc=0.890833\n",
      "Reloaded the best model.\n"
     ]
    }
   ],
   "source": [
    "from fastNLP import (Callback, EarlyStopCallback,\n",
    "                     Trainer, CrossEntropyLoss, AccuracyMetric)\n",
    "from fastNLP.models import CNNText\n",
    "import torch.cuda\n",
    "\n",
    "# prepare data\n",
    "def get_data():\n",
    "    from fastNLP.io import ChnSentiCorpPipe as pipe\n",
    "    data = pipe().process_from_file()\n",
    "    print(data)\n",
    "    data.rename_field('chars', 'words')\n",
    "    train_data = data.datasets['train']\n",
    "    dev_data = data.datasets['dev']\n",
    "    test_data = data.datasets['test']\n",
    "    vocab = data.vocabs['words']\n",
    "    tgt_vocab = data.vocabs['target']\n",
    "    return train_data, dev_data, test_data, vocab, tgt_vocab\n",
    "\n",
    "# prepare model\n",
    "train_data, dev_data, _, vocab, tgt_vocab = get_data()\n",
    "device = 'cuda:0' if torch.cuda.is_available() else 'cpu'\n",
    "model = CNNText((len(vocab),50), num_classes=len(tgt_vocab))\n",
    "\n",
    "# define callback\n",
    "callbacks=[EarlyStopCallback(5)]\n",
    "\n",
    "# pass callbacks to Trainer\n",
    "def train_with_callback(cb_list):\n",
    "    trainer = Trainer(\n",
    "        device=device,\n",
    "        n_epochs=3,\n",
    "        model=model, \n",
    "        train_data=train_data, \n",
    "        dev_data=dev_data, \n",
    "        loss=CrossEntropyLoss(),   \n",
    "        metrics=AccuracyMetric(), \n",
    "        callbacks=cb_list, \n",
    "        check_code_level=-1\n",
    "    )\n",
    "    trainer.train()\n",
    "\n",
    "train_with_callback(callbacks)"
   ]
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   "source": [
    "fastNLP 中的 Callback\n",
    "-------\n",
    "fastNLP 中提供了很多常用的 Callback，如梯度裁剪，训练时早停和测试验证集，fitlog 等等。具体 Callback 请参考 fastNLP.core.callbacks"
   ]
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     "text": [
      "training epochs started 2019-09-17-03-34-49\n"
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     "text": [
      "Evaluate data in 0.13 seconds!\n"
     ]
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     "text": [
      "Evaluate data in 0.12 seconds!\n",
      "Evaluation on data-test:\n",
      "AccuracyMetric: acc=0.890833\n",
      "Evaluation on dev at Epoch 1/3. Step:300/900: \n",
      "AccuracyMetric: acc=0.890833\n",
      "\n"
     ]
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     "text": [
      "Evaluate data in 0.09 seconds!\n"
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     "text": [
      "Evaluate data in 0.09 seconds!\n",
      "Evaluation on data-test:\n",
      "AccuracyMetric: acc=0.8875\n",
      "Evaluation on dev at Epoch 2/3. Step:600/900: \n",
      "AccuracyMetric: acc=0.8875\n",
      "\n"
     ]
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     "text": [
      "Evaluate data in 0.11 seconds!\n"
     ]
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     "text": [
      "Evaluate data in 0.1 seconds!\n",
      "Evaluation on data-test:\n",
      "AccuracyMetric: acc=0.885\n",
      "Evaluation on dev at Epoch 3/3. Step:900/900: \n",
      "AccuracyMetric: acc=0.885\n",
      "\n",
      "\r\n",
      "In Epoch:1/Step:300, got best dev performance:\n",
      "AccuracyMetric: acc=0.890833\n",
      "Reloaded the best model.\n"
     ]
    }
   ],
   "source": [
    "from fastNLP import EarlyStopCallback, GradientClipCallback, EvaluateCallback\n",
    "callbacks = [\n",
    "    EarlyStopCallback(5),\n",
    "    GradientClipCallback(clip_value=5, clip_type='value'),\n",
    "    EvaluateCallback(dev_data)\n",
    "]\n",
    "\n",
    "train_with_callback(callbacks)"
   ]
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   "source": [
    "自定义 Callback\n",
    "------\n",
    "\n",
    "这里我们以一个简单的 Callback作为例子，它的作用是打印每一个 Epoch 平均训练 loss。\n",
    "\n",
    "#### 创建 Callback\n",
    "    \n",
    "要自定义 Callback，我们要实现一个类，继承 fastNLP.Callback。\n",
    "\n",
    "这里我们定义 MyCallBack ，继承 fastNLP.Callback 。\n",
    "\n",
    "#### 指定 Callback 调用的阶段\n",
    "    \n",
    "Callback 中所有以 on_ 开头的类方法会在 Trainer 的训练中在特定阶段调用。 如 on_train_begin() 会在训练开始时被调用，on_epoch_end() 会在每个 epoch 结束时调用。 具体有哪些类方法，参见 Callback 文档。\n",
    "\n",
    "这里， MyCallBack 在求得loss时调用 on_backward_begin() 记录当前 loss ，在每一个 epoch 结束时调用 on_epoch_end() ，求当前 epoch 平均loss并输出。\n",
    "\n",
    "#### 使用 Callback 的属性访问 Trainer 的内部信息\n",
    "    \n",
    "为了方便使用，可以使用 Callback 的属性，访问 Trainer 中的对应信息，如 optimizer, epoch, n_epochs，分别对应训练时的优化器，当前 epoch 数，和总 epoch 数。 具体可访问的属性，参见文档 Callback 。\n",
    "\n",
    "这里， MyCallBack 为了求平均 loss ，需要知道当前 epoch 的总步数，可以通过 self.step 属性得到当前训练了多少步。\n",
    "\n"
   ]
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     "text": [
      "training epochs started 2019-09-17-03-42-58\n"
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     "text": [
      "Evaluate data in 0.11 seconds!\n",
      "Evaluation on dev at Epoch 1/3. Step:300/900: \n",
      "AccuracyMetric: acc=0.883333\n",
      "\n",
      "Avg loss at epoch 1, 0.100254\n"
     ]
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     "text": [
      "Evaluate data in 0.1 seconds!\n",
      "Evaluation on dev at Epoch 2/3. Step:600/900: \n",
      "AccuracyMetric: acc=0.8775\n",
      "\n",
      "Avg loss at epoch 2, 0.183511\n"
     ]
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     "text": [
      "Evaluate data in 0.13 seconds!\n",
      "Evaluation on dev at Epoch 3/3. Step:900/900: \n",
      "AccuracyMetric: acc=0.875833\n",
      "\n",
      "Avg loss at epoch 3, 0.257103\n",
      "\r\n",
      "In Epoch:1/Step:300, got best dev performance:\n",
      "AccuracyMetric: acc=0.883333\n",
      "Reloaded the best model.\n"
     ]
    }
   ],
   "source": [
    "from fastNLP import Callback\n",
    "from fastNLP import logger\n",
    "\n",
    "class MyCallBack(Callback):\n",
    "    \"\"\"Print average loss in each epoch\"\"\"\n",
    "    def __init__(self):\n",
    "        super().__init__()\n",
    "        self.total_loss = 0\n",
    "        self.start_step = 0\n",
    "    \n",
    "    def on_backward_begin(self, loss):\n",
    "        self.total_loss += loss.item()\n",
    "    \n",
    "    def on_epoch_end(self):\n",
    "        n_steps = self.step - self.start_step\n",
    "        avg_loss = self.total_loss / n_steps\n",
    "        logger.info('Avg loss at epoch %d, %.6f', self.epoch, avg_loss)\n",
    "        self.start_step = self.step\n",
    "\n",
    "callbacks = [MyCallBack()]\n",
    "train_with_callback(callbacks)"
   ]
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