# 动态图机制-DyGraph PaddlePaddle的DyGraph模式是一种动态的图执行机制，可以立即执行结果，无需构建整个图。同时，和以往静态的执行计算图不同，DyGraph模式下您的所有操作可以立即获得执行结果，而不必等待所构建的计算图全部执行完成，这样可以让您更加直观地构建PaddlePaddle下的深度学习任务，以及进行模型的调试，同时还减少了大量用于构建静态计算图的代码，使得您编写、调试网络的过程变得更加便捷。 PaddlePaddle DyGraph是一个更加灵活易用的模式，可提供： * 更加灵活便捷的代码组织结构： 使用python的执行控制流程和面向对象的模型设计 * 更加便捷的调试功能： 直接使用python的打印方法即时打印所需要的结果，从而检查正在运行的模型结果便于测试更改 * 和静态执行图通用的模型代码：同样的模型代码可以使用更加便捷的DyGraph调试，执行，同时也支持使用原有的静态图模式执行 ## 设置和基本用法 1. 升级到最新的PaddlePaddle 1.5: pip install -q --upgrade paddlepaddle==1.5 2. 使用`fluid.dygraph.guard(place=None)` 上下文： import paddle.fluid as fluid with fluid.dygraph.guard(): # write your executable dygraph code here 现在您就可以在`fluid.dygraph.guard()`上下文环境中使用DyGraph的模式运行网络了，DyGraph将改变以往PaddlePaddle的执行方式： 现在他们将会立即执行，并且将计算结果返回给Python。 Dygraph将非常适合和Numpy一起使用，使用`fluid.dygraph.to_variable(x)`将会将ndarray转换为`fluid.Variable`，而使用`fluid.Variable.numpy()`将可以把任意时刻获取到的计算结果转换为Numpy`ndarray`： x = np.ones([2, 2], np.float32) with fluid.dygraph.guard(): inputs = [] for _ in range(10): inputs.append(fluid.dygraph.to_variable(x)) ret = fluid.layers.sums(inputs) print(ret.numpy()) [[10. 10.] [10. 10.]] Process finished with exit code 0 > 这里创建了一系列`ndarray`的输入，执行了一个`sum`操作之后，我们可以直接将运行的结果打印出来 然后通过调用`reduce_sum`后使用`Variable.backward()`方法执行反向，使用`Variable.gradient()`方法即可获得反向网络执行完成后的梯度值的`ndarray`形式： loss = fluid.layers.reduce_sum(ret) loss.backward() print(loss.gradient()) 得到输出 ： [1.] Process finished with exit code 0 ## 基于DyGraph构建网络 1. 编写一段用于DyGraph执行的Object-Oriented-Designed, PaddlePaddle模型代码主要由以下**三个部分**组成： **请注意，如果您设计的这一层结构是包含参数的，则必须要使用继承自`fluid.dygraph.Layer`的Object-Oriented-Designed的类来描述该层的行为。** 1. 建立一个可以在DyGraph模式中执行的，Object-Oriented的网络，需要继承自`fluid.dygraph.Layer`，其中需要调用基类的`__init__`方法，并且实现带有参数`name_scope`（用来标识本层的名字）的`__init__`构造函数，在构造函数中，我们通常会执行一些例如参数初始化，子网络初始化的操作，执行这些操作时不依赖于输入的动态信息: class MyLayer(fluid.dygraph.Layer): def __init__(self, name_scope): super(MyLayer, self).__init__(name_scope) 2. 实现一个`forward(self, *inputs)`的执行函数，该函数将负责执行实际运行时网络的执行逻辑， 该函数将会在每一轮训练/预测中被调用，这里我们将执行一个简单的`relu` -> `elementwise add` -> `reduce sum`： def forward(self, inputs): x = fluid.layers.relu(inputs) self._x_for_debug = x x = fluid.layers.elementwise_mul(x, x) x = fluid.layers.reduce_sum(x) return [x] 2. 在`fluid.dygraph.guard()`中执行： 1. 使用Numpy构建输入： np_inp = np.array([1.0, 2.0, -1.0], dtype=np.float32) 2. 转换输入的`ndarray`为`Variable`, 并执行前向网络获取返回值： 使用`fluid.dygraph.to_variable(np_inp)`转换Numpy输入为DyGraph接收的输入，然后使用`my_layer(var_inp)[0]`调用callable object并且获取了`x`作为返回值，利用`x.numpy()`方法直接获取了执行得到的`x`的`ndarray`返回值。 with fluid.dygraph.guard(): var_inp = fluid.dygraph.to_variable(np_inp) my_layer = MyLayer("my_layer") x = my_layer(var_inp)[0] dy_out = x.numpy() 3. 计算梯度：自动微分对于实现机器学习算法（例如用于训练神经网络的反向传播）来说很有用， 使用`x.backward()`方法可以从某个`fluid.Varaible`开始执行反向网络，同时利用`my_layer._x_for_debug.gradient()`获取了网络中`x`梯度的`ndarray` 返回值： x.backward() dy_grad = my_layer._x_for_debug.gradient() 完整代码如下： import paddle.fluid as fluid import numpy as np class MyLayer(fluid.dygraph.Layer): def __init__(self, name_scope): super(MyLayer, self).__init__(name_scope) def forward(self, inputs): x = fluid.layers.relu(inputs) self._x_for_debug = x x = fluid.layers.elementwise_mul(x, x) x = fluid.layers.reduce_sum(x) return [x] if __name__ == '__main__': np_inp = np.array([1.0, 2.0, -1.0], dtype=np.float32) with fluid.dygraph.guard(): var_inp = fluid.dygraph.to_variable(np_inp) my_layer = MyLayer("my_layer") x = my_layer(var_inp)[0] dy_out = x.numpy() x.backward() dy_grad = my_layer._x_for_debug.gradient() my_layer.clear_gradients() # 将参数梯度清零以保证下一轮训练的正确性 ## 使用DyGraph训练模型 接下来我们将以“手写数字识别”这个最基础的模型为例，展示如何利用DyGraph模式搭建并训练一个模型： 有关手写数字识别的相关理论知识请参考[PaddleBook](https://github.com/PaddlePaddle/book/tree/develop/02.recognize_digits)中的内容，我们在这里默认您已经了解了该模型所需的深度学习理论知识。 1. 准备数据，我们使用`paddle.dataset.mnist`作为训练所需要的数据集： train_reader = paddle.batch( paddle.dataset.mnist.train(), batch_size=BATCH_SIZE, drop_last=True) 2. 构建网络，虽然您可以根据之前的介绍自己定义所有的网络结构，但是您也可以直接使用`fluid.dygraph.Layer`当中我们为您定制好的一些基础网络结构，这里我们利用`fluid.dygraph.Conv2D`以及`fluid.dygraph.Pool2d`构建了基础的`SimpleImgConvPool`： class SimpleImgConvPool(fluid.dygraph.Layer): def __init__(self, name_scope, num_filters, filter_size, pool_size, pool_stride, pool_padding=0, pool_type='max', global_pooling=False, conv_stride=1, conv_padding=0, conv_dilation=1, conv_groups=1, act=None, use_cudnn=False, param_attr=None, bias_attr=None): super(SimpleImgConvPool, self).__init__(name_scope) self._conv2d = fluid.dygraph.Conv2D( self.full_name(), num_filters=num_filters, filter_size=filter_size, stride=conv_stride, padding=conv_padding, dilation=conv_dilation, groups=conv_groups, param_attr=None, bias_attr=None, act=act, use_cudnn=use_cudnn) self._pool2d = fluid.dygraph.Pool2D( self.full_name(), pool_size=pool_size, pool_type=pool_type, pool_stride=pool_stride, pool_padding=pool_padding, global_pooling=global_pooling, use_cudnn=use_cudnn) def forward(self, inputs): x = self._conv2d(inputs) x = self._pool2d(x) return x > 注意: 构建网络时子网络的定义和使用请在`__init__`中进行， 而子网络的执行则在`forward`函数中进行 3. 利用已经构建好的`SimpleImgConvPool`组成最终的`MNIST`网络： class MNIST(fluid.dygraph.Layer): def __init__(self, name_scope): super(MNIST, self).__init__(name_scope) self._simple_img_conv_pool_1 = SimpleImgConvPool( self.full_name(), 20, 5, 2, 2, act="relu") self._simple_img_conv_pool_2 = SimpleImgConvPool( self.full_name(), 50, 5, 2, 2, act="relu") pool_2_shape = 50 * 4 * 4 SIZE = 10 scale = (2.0 / (pool_2_shape**2 * SIZE))**0.5 self._fc = fluid.dygraph.FC(self.full_name(), 10, param_attr=fluid.param_attr.ParamAttr( initializer=fluid.initializer.NormalInitializer( loc=0.0, scale=scale)), act="softmax") def forward(self, inputs, label=None): x = self._simple_img_conv_pool_1(inputs) x = self._simple_img_conv_pool_2(x) x = self._fc(x) if label is not None: acc = fluid.layers.accuracy(input=x, label=label) return x, acc else: return x 4. 在`fluid.dygraph.guard()`中定义配置好的`MNIST`网络结构，此时即使没有训练也可以在`fluid.dygraph.guard()`中调用模型并且检查输出： with fluid.dygraph.guard(): mnist = MNIST("mnist") id, data = list(enumerate(train_reader()))[0] dy_x_data = np.array( [x[0].reshape(1, 28, 28) for x in data]).astype('float32') img = fluid.dygraph.to_variable(dy_x_data) print("result is: {}".format(mnist(img).numpy())) result is: [[0.10135901 0.1051138 0.1027941 ... 0.0972859 0.10221873 0.10165327] [0.09735426 0.09970362 0.10198303 ... 0.10134517 0.10179105 0.10025002] [0.09539858 0.10213123 0.09543551 ... 0.10613529 0.10535969 0.097991 ] ... [0.10120598 0.0996111 0.10512722 ... 0.10067689 0.10088114 0.10071224] [0.09889644 0.10033772 0.10151272 ... 0.10245881 0.09878646 0.101483 ] [0.09097178 0.10078511 0.10198414 ... 0.10317434 0.10087223 0.09816764]] Process finished with exit code 0 5. 构建训练循环，在每一轮参数更新完成后我们调用`mnist.clear_gradients()`来重置梯度： with fluid.dygraph.guard(): epoch_num = 5 BATCH_SIZE = 64 train_reader = paddle.batch( paddle.dataset.mnist.train(), batch_size=32, drop_last=True) mnist = MNIST("mnist") id, data = list(enumerate(train_reader()))[0] adam = fluid.optimizer.AdamOptimizer(learning_rate=0.001) for epoch in range(epoch_num): for batch_id, data in enumerate(train_reader()): dy_x_data = np.array([x[0].reshape(1, 28, 28) for x in data]).astype('float32') y_data = np.array( [x[1] for x in data]).astype('int64').reshape(-1, 1) img = fluid.dygraph.to_variable(dy_x_data) label = fluid.dygraph.to_variable(y_data) cost = mnist(img) loss = fluid.layers.cross_entropy(cost, label) avg_loss = fluid.layers.mean(loss) if batch_id % 100 == 0 and batch_id is not 0: print("epoch: {}, batch_id: {}, loss is: {}".format(epoch, batch_id, avg_loss.numpy())) avg_loss.backward() adam.minimize(avg_loss) mnist.clear_gradients() 6. 变量及优化器 模型的参数或者任何您希望检测的值可以作为变量封装在类中，然后通过对象获取并使用`numpy()`方法获取其`ndarray`的输出， 在训练过程中您可以使用`mnist.parameters()`来获取到网络中所有的参数，也可以指定某一个`Layer`的某个参数或者`parameters()`来获取该层的所有参数，使用`numpy()`方法随时查看参数的值 反向运行后调用之前定义的`Adam`优化器对象的`minimize`方法进行参数更新: with fluid.dygraph.guard(): epoch_num = 5 BATCH_SIZE = 64 mnist = MNIST("mnist") adam = fluid.optimizer.AdamOptimizer(learning_rate=0.001) train_reader = paddle.batch( paddle.dataset.mnist.train(), batch_size= BATCH_SIZE, drop_last=True) np.set_printoptions(precision=3, suppress=True) for epoch in range(epoch_num): for batch_id, data in enumerate(train_reader()): dy_x_data = np.array( [x[0].reshape(1, 28, 28) for x in data]).astype('float32') y_data = np.array( [x[1] for x in data]).astype('int64').reshape(BATCH_SIZE, 1) img = fluid.dygraph.to_variable(dy_x_data) label = fluid.dygraph.to_variable(y_data) label.stop_gradient = True cost = mnist(img) loss = fluid.layers.cross_entropy(cost, label) avg_loss = fluid.layers.mean(loss) dy_out = avg_loss.numpy() avg_loss.backward() adam.minimize(avg_loss) mnist.clear_gradients() dy_param_value = {} for param in mnist.parameters(): dy_param_value[param.name] = param.numpy() if batch_id % 20 == 0: print("Loss at step {}: {}".format(batch_id, avg_loss.numpy())) print("Final loss: {}".format(avg_loss.numpy())) print("_simple_img_conv_pool_1_conv2d W's mean is: {}".format(mnist._simple_img_conv_pool_1._conv2d._filter_param.numpy().mean())) print("_simple_img_conv_pool_1_conv2d Bias's mean is: {}".format(mnist._simple_img_conv_pool_1._conv2d._bias_param.numpy().mean())) Loss at step 0: [2.302] Loss at step 20: [1.616] Loss at step 40: [1.244] Loss at step 60: [1.142] Loss at step 80: [0.911] Loss at step 100: [0.824] Loss at step 120: [0.774] Loss at step 140: [0.626] Loss at step 160: [0.609] Loss at step 180: [0.627] Loss at step 200: [0.466] Loss at step 220: [0.499] Loss at step 240: [0.614] Loss at step 260: [0.585] Loss at step 280: [0.503] Loss at step 300: [0.423] Loss at step 320: [0.509] Loss at step 340: [0.348] Loss at step 360: [0.452] Loss at step 380: [0.397] Loss at step 400: [0.54] Loss at step 420: [0.341] Loss at step 440: [0.337] Loss at step 460: [0.155] Final loss: [0.164] _simple_img_conv_pool_1_conv2d W's mean is: 0.00606656912714 _simple_img_conv_pool_1_conv2d Bias's mean is: -3.4576318285e-05 7. 性能 在使用`fluid.dygraph.guard()`时可以通过传入`fluid.CUDAPlace(0)`或者`fluid.CPUPlace()`来选择执行DyGraph的设备，通常如果不做任何处理将会自动适配您的设备。 ## 模型参数的保存 
在模型训练中可以使用` fluid.dygraph.save_persistables(your_model_object.state_dict(), "save_dir", optimizers=None)`来保存`your_model_object`中所有的模型参数, 以及使用`learning rate decay`的优化器。也可以自定义需要保存的“参数名” - “参数对象”的Python Dictionary传入。 同样可以使用`models，optimizers = fluid.dygraph.load_persistables("save_dir")`获取保存的模型参数和优化器。 再使用`your_modle_object.load_dict(models)`接口来恢复保存的模型参数从而达到继续训练的目的。 以及使用`your_optimizer_object.load(optimizers)`接口来恢复保存的优化器中的`learning rate decay`值 下面的代码展示了如何在“手写数字识别”任务中保存参数并且读取已经保存的参数来继续训练。 with fluid.dygraph.guard(): epoch_num = 5 BATCH_SIZE = 64 mnist = MNIST("mnist") adam = fluid.optimizer.Adam(learning_rate=0.001) train_reader = paddle.batch( paddle.dataset.mnist.train(), batch_size= BATCH_SIZE, drop_last=True) np.set_printoptions(precision=3, suppress=True) dy_param_init_value={} for epoch in range(epoch_num): for batch_id, data in enumerate(train_reader()): dy_x_data = np.array( [x[0].reshape(1, 28, 28) for x in data]).astype('float32') y_data = np.array( [x[1] for x in data]).astype('int64').reshape(BATCH_SIZE, 1) img = fluid.dygraph.to_variable(dy_x_data) label = fluid.dygraph.to_variable(y_data) label.stop_gradient = True cost = mnist(img) loss = fluid.layers.cross_entropy(cost, label) avg_loss = fluid.layers.mean(loss) dy_out = avg_loss.numpy() avg_loss.backward() adam.minimize(avg_loss) if batch_id == 20: fluid.dygraph.save_persistables(mnist.state_dict(), "save_dir", adam) mnist.clear_gradients() if batch_id == 20: for param in mnist.parameters(): dy_param_init_value[param.name] = param.numpy() model, _ = fluid.dygraph.load_persistables("save_dir") mnist.load_dict(model) break if epoch == 0: break restore = mnist.parameters() # check save and load success = True for value in restore: if (not np.array_equal(value.numpy(), dy_param_init_value[value.name])) or (not np.isfinite(value.numpy().all())) or (np.isnan(value.numpy().any())): success = False print("model save and load success? {}".format(success)) ## 模型评估 当我们需要在DyGraph模式下利用搭建的模型进行预测任务，可以使用`YourModel.eval()`接口，在之前的手写数字识别模型中我们使用`mnist.eval()`来启动预测模式（我们默认在`fluid.dygraph.guard()`上下文中是训练模式），在预测的模式下，DyGraph将只会执行前向的预测网络，而不会进行自动求导并执行反向网络： 下面的代码展示了如何使用DyGraph模式训练一个用于执行“手写数字识别”任务的模型并保存，并且利用已经保存好的模型进行预测。 我们在`fluid.dygraph.guard()`上下文中进行了模型的保存和训练，值得注意的是，当我们需要在训练的过程中进行预测时需要使用`YourModel.eval()`切换到预测模式，并且在预测完成后使用`YourModel.train()`切换回训练模式继续训练。 我们在`inference_mnist `中启用另一个`fluid.dygraph.guard()`，并在其上下文中`load`之前保存的`checkpoint`进行预测，同样的在执行预测前需要使用`YourModel.eval()`来切换到预测模式。 def test_mnist(reader, model, batch_size): acc_set = [] avg_loss_set = [] for batch_id, data in enumerate(reader()): dy_x_data = np.array([x[0].reshape(1, 28, 28) for x in data]).astype('float32') y_data = np.array( [x[1] for x in data]).astype('int64').reshape(batch_size, 1) img = fluid.dygraph.to_variable(dy_x_data) label = fluid.dygraph.to_variable(y_data) label.stop_gradient = True prediction, acc = model(img, label) loss = fluid.layers.cross_entropy(input=prediction, label=label) avg_loss = fluid.layers.mean(loss) acc_set.append(float(acc.numpy())) avg_loss_set.append(float(avg_loss.numpy())) # get test acc and loss acc_val_mean = np.array(acc_set).mean() avg_loss_val_mean = np.array(avg_loss_set).mean() return avg_loss_val_mean, acc_val_mean def inference_mnist(): with fluid.dygraph.guard(): mnist_infer = MNIST("mnist") # load checkpoint model_dict, _ = fluid.dygraph.load_persistables("save_dir") mnist_infer.load_dict(model_dict) print("checkpoint loaded") # start evaluate mode mnist_infer.eval() def load_image(file): im = Image.open(file).convert('L') im = im.resize((28, 28), Image.ANTIALIAS) im = np.array(im).reshape(1, 1, 28, 28).astype(np.float32) im = im / 255.0 * 2.0 - 1.0 return im cur_dir = os.path.dirname(os.path.realpath(__file__)) tensor_img = load_image(cur_dir + '/image/infer_3.png') results = mnist_infer(fluid.dygraph.to_variable(tensor_img)) lab = np.argsort(results.numpy()) print("Inference result of image/infer_3.png is: %d" % lab[0][-1]) with fluid.dygraph.guard(): epoch_num = 1 BATCH_SIZE = 64 mnist = MNIST("mnist") adam = fluid.optimizer.AdamOptimizer(learning_rate=0.001) test_reader = paddle.batch( paddle.dataset.mnist.test(), batch_size=BATCH_SIZE, drop_last=True) train_reader = paddle.batch( paddle.dataset.mnist.train(), batch_size=BATCH_SIZE, drop_last=True) for epoch in range(epoch_num): for batch_id, data in enumerate(train_reader()): dy_x_data = np.array([x[0].reshape(1, 28, 28) for x in data]).astype('float32') y_data = np.array( [x[1] for x in data]).astype('int64').reshape(-1, 1) img = fluid.dygraph.to_variable(dy_x_data) label = fluid.dygraph.to_variable(y_data) label.stop_gradient = True cost, acc = mnist(img, label) loss = fluid.layers.cross_entropy(cost, label) avg_loss = fluid.layers.mean(loss) avg_loss.backward() adam.minimize(avg_loss) # save checkpoint mnist.clear_gradients() if batch_id % 100 == 0: print("Loss at epoch {} step {}: {:}".format( epoch, batch_id, avg_loss.numpy())) mnist.eval() test_cost, test_acc = test_mnist(test_reader, mnist, BATCH_SIZE) mnist.train() print("Loss at epoch {} , Test avg_loss is: {}, acc is: {}".format( epoch, test_cost, test_acc)) fluid.dygraph.save_persistables(mnist.state_dict(), "save_dir") print("checkpoint saved") inference_mnist() Loss at epoch 0 step 0: [2.2991252] Loss at epoch 0 step 100: [0.15491392] Loss at epoch 0 step 200: [0.13315125] Loss at epoch 0 step 300: [0.10253005] Loss at epoch 0 step 400: [0.04266362] Loss at epoch 0 step 500: [0.08894891] Loss at epoch 0 step 600: [0.08999012] Loss at epoch 0 step 700: [0.12975612] Loss at epoch 0 step 800: [0.15257305] Loss at epoch 0 step 900: [0.07429226] Loss at epoch 0 , Test avg_loss is: 0.05995981965082674, acc is: 0.9794671474358975 checkpoint saved No optimizer loaded. If you didn't save optimizer, please ignore this. The program can still work with new optimizer. checkpoint loaded Inference result of image/infer_3.png is: 3 ## 编写兼容的模型 以上一步中手写数字识别的例子为例，动态图的模型代码可以直接用于静态图中作为模型代码，执行时，直接使用PaddlePaddle静态图执行方式即可，这里以静态图中的`executor`为例, 模型代码可以直接使用之前的模型代码，执行时使用`Executor`执行即可 epoch_num = 1 BATCH_SIZE = 64 exe = fluid.Executor(fluid.CPUPlace()) mnist = MNIST("mnist") sgd = fluid.optimizer.SGDOptimizer(learning_rate=1e-3) train_reader = paddle.batch( paddle.dataset.mnist.train(), batch_size=BATCH_SIZE, drop_last=True) img = fluid.layers.data( name='pixel', shape=[1, 28, 28], dtype='float32') label = fluid.layers.data(name='label', shape=[1], dtype='int64') cost = mnist(img) loss = fluid.layers.cross_entropy(cost, label) avg_loss = fluid.layers.mean(loss) sgd.minimize(avg_loss) out = exe.run(fluid.default_startup_program()) for epoch in range(epoch_num): for batch_id, data in enumerate(train_reader()): static_x_data = np.array( [x[0].reshape(1, 28, 28) for x in data]).astype('float32') y_data = np.array( [x[1] for x in data]).astype('int64').reshape([BATCH_SIZE, 1]) fetch_list = [avg_loss.name] out = exe.run( fluid.default_main_program(), feed={"pixel": static_x_data, "label": y_data}, fetch_list=fetch_list) static_out = out[0] if batch_id % 100 == 0 and batch_id is not 0: print("epoch: {}, batch_id: {}, loss: {}".format(epoch, batch_id, static_out))