$ wget -c https://github.com/scikit-learn/scikit-learn/archive/0.20.X.zip # 下载 scikit-learn 0.20.x 源码
$ wget -c https://files.pythonhosted.org/packages/0f/d7/136a447295adade38e7184618816e94190ded028318062a092daeb972073/scikit-learn-0.20.0.tar.gz # https://pypi.org/project/scikit-learn/#files
$ tar xzvf scikit-learn-0.20.0.tar.gz # 如果从 pypi.org 下载就用这条命令解压
$ unzip 0.20.X.zip # 解压到当前目录
$ cd scikit-learn-0.20.X/
$ python3 -m venv sklearn0.20.x # 创建 sklearn 的虚拟环境
$ source sklearn0.20.x/bin/activate # 激活虚拟环境
(sklearn0.20.x) $ pip install numpy scipy cython pytest matplotlib # 安装依赖
(sklearn0.20.x) $ pip install --editable . # 安装 sklearn
(sklearn0.20.x) $ pytest sklearn
