Windows系统下安装apex，及错误汇总

官网地址：NVIDIA/apex: A PyTorch Extension: Tools for easy mixed precision and distributed training in Pytorch (github.com)https://github.com/NVIDIA/apex
官方说支持Ubuntu系统，Windows只是实验性的，所以在windows上安装可能会遇到各种问题，本文不能涵盖所有问题。

方法1：直接安装

pip install apex

此指令会安装最新的apex 0.9以上版本，我遇到了如下错误：

WARNING: Building wheel for cryptacular failed: [Errno 2] No such file or directory: 'C:\\Users\\XXX\\AppData\\Local\\Temp\\pip-wheel-0dhfjrr3\\cryptacular-1.6.2-cp37-cp37m-win_amd64.whl'
Failed to build cryptacular
ERROR: Could not build wheels for cryptacular, which is required to install pyproject.toml-based projects

方法2：下载安装

git clone https://www.github.com/nvidia/apex
cd apex
python setup.py install

这样会安装apex 0.1版本，理想情况下就安装成功了，我遇到了错误汇总：

module 'torch.nn' has no attribute 'backends'  这个应该是CUDA版本和apex兼容问题

或者错误

AttributeError: module 'torch.distributed' has no attribute '_all_gather_base'

 方法3：下载安装

git clone https://github.com/NVIDIA/apex
cd apex
pip install -v --no-cache-dir --global-option="--cpp_ext" --global-option="--cuda_ext" ./

或者
python setup.py install --cuda_ext --cpp_ext ./

还是遇到错误，

1 error detected in the compilation of "csrc/multi_tensor_scale_kernel.cu"

或者错误

ImportError was: ModuleNotFoundError("No module named 'amp_C'")

 方法4：成功版本

git clone https://github.com/NVIDIA/apex.git
cd apex
git checkout f3a960f80244cf9e80558ab30f7f7e8cbf03c0a0
python setup.py install --cuda_ext --cpp_ext