python
__init__.py
导入包时实际导入的是__init__.py，可以通过__init__.py来控制可以使用的包和函数。
__all__关键字可以方便得用来指定要导入的包。
ctypes
cffi的wraper
cffi
pytorch
c文件
需要一个h文件
python文件
build so
ffi.create_extension和build
扩展autograd
需要init forward 和 backward
tensor和variable的函数基本一样
function的属性
Attributes:
saved_tensors: Tuple of Tensors that were saved in the call to
:func:forward.
saved_variables: Tuple of Variables that correspond to the tensors
saved in the call to :func:forward.
needs_input_grad: Tuple of booleans of length :attr:num_inputs,
indicating whether a given input requires gradient. This can be
used to optimize buffers saved for backward, and ignoring gradient
computation in :func:~Function.backward.
num_inputs: Number of inputs given to :func:forward.
num_outputs: Number of tensors returned by :func:forward.
requires_grad: Boolean indicating whether the :func:backward will
ever need to be called.
扩展nn
modules版本
可以保存参数
需要init（用于初始化参数） forward（调用autograd即可）