Latest pyyaml expecting class but getting function #840（配置detectron时，遇到的一个坑，导致加载模型时报错）

Hi,
I am not sure if the issue is with you or pyyaml but I just completed a clean build and get the following error when running infer_simple.py example with pyyaml version 5.1

yaml.constructor.ConstructorError: while constructing a Python instance expected a class, but found <class 'builtin_function_or_method'> in "<unicode string>", line 3, column 20: BBOX_XFORM_CLIP: !!python/object/apply:numpy.core ...

I rolled the version back to 4.2 and it works fine:
pip install pyyaml==4.2b2

配置detectron时，遇到的一个坑，导致加载模型时报错，原来是因为pyyaml版本太高，降到4.2b2版本即可