直接用pip install scikit-learn，报错如下：
Contents of anaconda3/envs/pyt/lib/python3.7/site-packages/sklearn/__check_build:
pycache init.py _check_build.cpython-37m-x86_64-linux-gnu.so
setup.py
It seems that scikit-learn has not been built correctly.
If you have installed scikit-learn from source, please do not forget
to build the package before using it: run python setup.py install or
make in the source directory.
If you have used an installer, please check that it is suited for your
Python version, your operating system and your platform.
加上版本号，成功
pip install scikit-learn==0.20.1
