What does this mean? Some installed kegs have no formulae

Question

I see this after typing in "brew doctor"

Warning: Some installed kegs have no formulae! This means they were either deleted or installed with brew diy. You should find replacements for the following formulae:
python@2

What does this mean and how do I fix it?

Answer 1

It's just a warning, as most "brew doctor" messages are. Python 2 is dead. You can remove it with brew uninstall python@2.