Simplest way to add in a syntax rule

Question

I would like to add in the following rule to my syntax to help with python files:

:syn match pythonBoolean "\<self\ze\."
:hi pythonBoolean cterm=bold

It works when I type it in directly to the file:

However, for the life of me, I cannot figure out how to have this as a default setting -- I've tried putting it in my vimrc, in an after folder, in a syntax file, etc. etc. but each time I get some error or other and it never ends up actually working properly.

What would be the simplest way to add the above two lines so that it will mark-up my python file with those changes (like it does when I enter it in directly)?

Answer 1

Try using ~/.vim/after/syntax/python.vim:

syn match pythonSelf "\<self\.\@="
hi pythonSelf cterm=bold

I used a slightly different syntax group so you could customize it more; you could also hi link it to another group if you wanted.