PyLayerContext¶

class paddle.autograd. PyLayerContext [源代码] ¶

PyLayerContext 对象能够辅助 PyLayer 实现某些功能。

示例代码

         import paddle
from paddle.autograd import PyLayer

class cus_tanh(PyLayer):
    @staticmethod
    def forward(ctx, x):
        # ctx is a object of PyLayerContext.
        y = paddle.tanh(x)
        ctx.save_for_backward(y)
        return y

    @staticmethod
    def backward(ctx, dy):
        # ctx is a object of PyLayerContext.
        y, = ctx.saved_tensor()
        grad = dy * (1 - paddle.square(y))
        return grad

        

save_for_backward ( self, *tensors ) ¶

用于暂存 backward 需要的 Tensor ，在 backward 中调用 saved_tensor 获取这些 Tensor 。

注解

这个API只能被调用一次，且只能在 forward 中调用。

参数¶

tensors (list of Tensor) - 需要被暂存的 Tensor

返回：None

示例代码

          import paddle
from paddle.autograd import PyLayer

class cus_tanh(PyLayer):
    @staticmethod
    def forward(ctx, x):
        # ctx is a context object that store some objects for backward.
        y = paddle.tanh(x)
        # Pass tensors to backward.
        ctx.save_for_backward(y)
        return y

    @staticmethod
    def backward(ctx, dy):
        # Get the tensors passed by forward.
        y, = ctx.saved_tensor()
        grad = dy * (1 - paddle.square(y))
        return grad

         

saved_tensor ( self, *tensors ) ¶

获取被 save_for_backward 暂存的 Tensor 。

返回：如果调用 save_for_backward 暂存了一些 Tensor ，则返回这些 Tensor ，否则，返回 None。

示例代码

          import paddle
from paddle.autograd import PyLayer

class cus_tanh(PyLayer):
    @staticmethod
    def forward(ctx, x):
        # ctx is a context object that store some objects for backward.
        y = paddle.tanh(x)
        # Pass tensors to backward.
        ctx.save_for_backward(y)
        return y

    @staticmethod
    def backward(ctx, dy):
        # Get the tensors passed by forward.
        y, = ctx.saved_tensor()
        grad = dy * (1 - paddle.square(y))
        return grad

         