Jupyter notebook中Python2和Python3共存

我之前Jupyter notebook中只有Python3，可以通過一下方式添加python2:

python2 -m pip install ipykernel
python2 -m ipykernel install --user

python2是你的系統上對應的python2的命令，我的python2的命令是python，故對應的命令是：

python -m pip install ipykernel
python -m ipykernel install --user

與之對應，若之前Jupyter notebook中有Python2，要添加python3:

python3 -m pip install ipykernel
python3 -m ipykernel install --user

參考：https://stackoverflow.com/questions/30492623/using-both-python-2-x-and-python-3-x-in-ipython-notebook