Here is a quick guide on installing Python3 on a mac

Installation

brew update
brew upgrade
sudo mkdir -p /usr/local/Frameworks
sudo chown -R $(whoami) /usr/local/* 
brew install python3
brew link python3
brew doctor

Aliasing

 echo "alias python=/usr/local/bin/python3.7" >> ~/.zshrc

or

echo "alias python=/usr/local/bin/python3.7" >> ~/.bashrc

You could probably have just done this as well

alias python='python3'
alias pip='pip3'

I hope this is useful