After a few weeks sorting up and working with Python3 on my Mac Book Pro, the brew update failed to update and reported an error of aws command not found.
> brew update
The solution is straight through. Since aws cli is not found, it is a missed step in migrating Mac development environment from Python2 to Python3 -- the corresponding aws cli is not installed well to Python3.
My python environment is managed via PyEnv. When a new python version is installed, the upstream depeendencies are not maintained via requirement.txt so it needs a manual step to re-enable awscli.
>pip3 install awscli --upgrade