1.Python init.py 作用详解 link: can be used to import func in different dir.
2.python Numpy cs213_numpy
py -2 # run in python 2 env
py -3 # run in python 3 env
py -2 -m pip install package_name # install packages or '.whl file' in python 2 env
py -3 -m pip install package_name # '-m' stands for 'running pip module'