一、 No module named pip
如果在执行pip install --upgrade pip命令提示更新失败或是警告，再次使用pip提示“ModuleNotFoundError: No module named 'pip' ”错误；
1 执行第一条命令：
python -m ensurepip
2 执行第二条命令：
python -m pip install --upgrade pip
参考
二 ipython 安装和更新
pip install ipython
pip install --upgrade ipython
pip install --upgrade pip
不管是用pip装什么模块，前面都尽量不要加sudo，
三 Failed to start the Kernel.
Jupyter notebook中使用Markdown画流程图
试图安装nb-mermaid结果把Jupyter notebook搞挂了，kernal启动不了，
是因为nb-mermaid把ipython给降级了。通过（pip install --upgrade ipython）修复Jupyter notebook。
参考
Failed to start the Kernel. AttributeError: module 'collections' has no attribute 'MutableMapping'. View Jupyter log for further details.
ERROR: pip's dependency resolver does not currently take into account all the packages that are installed. This behaviour is the source of the following dependency conflicts. ipykernel 6.11.0 requires ipython>=7.23.1, but you have ipython 3.2.3 which is incompatible.
