[FEATURE] macos use python3 globally

[noelmcloughlin]

In bootstrap, consider setting MacOS to python3 using pyenv
Ref: https://opensource.com/article/19/5/python-3-default-mac#what-to-do
To bypass ld: symbol(s) not found for architecture x86_64 or clang errors here is full procedure.

brew uninstall --force binutils
brew uninstall --force pyenv
brew install --HEAD pyenv 
pyenv install 3.7.3
pyenv global 3.7.3
pyenv version
$ echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n  eval "$(pyenv init -)"\nfi' >> ~/.zshrc
$ echo -e 'if command -v pyenv 1>/dev/null 2>&1; then\n  eval "$(pyenv init -)"\nfi' >> ~/.bashrc

[noelmcloughlin]

% python --version
Python 3.7.3

% which python
/Users/noel/.pyenv/shims/python

% cat /Users/noel/.pyenv/version
3.7.3