[mcj]”ImportError: cannot import name ‘_C'”

出现："ImportError: cannot import name '_C'"，请build并且install detectron2。

安装方法：

Requirements

• Linux or macOS
• Python ≥ 3.6
• PyTorch ≥ 1.3
• torchvision that matches the PyTorch installation. You can install them together at pytorch.org to make sure of this.
• OpenCV, optional, needed by demo and visualization
• pycocotools: pip install cython; pip install 'git+https://github.com/cocodataset/cocoapi.git#subdirectory=PythonAPI'
• gcc & g++ ≥ 4.9

具有以上依赖性之后，运行：

pip install 'git+https://github.com/facebookresearch/detectron2.git'
# (add --user if you don't have permission)

# Or, to install it from a local clone:
git clone https://github.com/facebookresearch/detectron2.git
cd detectron2 && pip install -e .

# Or if you are on macOS
# MACOSX_DEPLOYMENT_TARGET=10.9 CC=clang CXX=clang++ pip install -e .

一般来说，重装pytorch之后，需要重新安装detectron2.