How to change syntax highlighting for mode?

Question

I've been able to partially modify how emacs highlights syntax of python files. For example I find highlighting the definition of variable to be disturbing and I've done this

'(font-lock-constant-face ((t (:foreground "#2aa198" :weight normal))))
 '(font-lock-keyword-face ((t (:foreground "#859900" :weight normal))))
 '(font-lock-variable-name-face ((t (:foreground "#839496")))))

But I'd also like imports to be highlighted with different color, stop highlighting "sys.exit()" as a constant etc, treat print as a builtin function, not as keyword etc. So I need to change how emacs parses python code. In vim you can do this by creating a custom syntax file and placing it in special folder, how to do the same for emacs?

from abc import ABC
print('some')
map(int, ('1',))
int('1')


@cached
def name(a, abc='abc'):
    pass

name(1, abc='bca')

The right one is how I want syntax highlighting to look and the left one is emacs.

Answer 1

In Emacs, syntax highlighting is performed using the module font-lock. It highlights a buffer in two phases:

• The syntactic phase, where comments and strings are highlighted.
• The keyword phase, where everything else is highlighted.

The rules for the keywords phase is stored in the variable font-lock-keywords. The variable accepts a complex data structure. It is fully described in it's doc string. However, the text is very complex, and it might take some time to let everything sink in -- I've been trying to understand it for the past 20 years ;-)

A keyword can either be based on a regexp or lisp code.

You can add font-lock keywords using font-lock-add-keywords and remove old ones using font-lock-remove-keywords. They take two arguments, a major mode and a list of new keywords. Instead of a major mode, you can pass nil, which makes them act on the current buffer. I would recommend you to use the latter method, as it would allow you to try out keyword variants until you are satisfied -- just kill the current buffer and reopen the file.

In your case, you will need to find the font-lock keywords that doesn't work as you want (e.g. how it highlights the @ sign, and how it decides which color a builtin function like print) and modify those.

The view and understand existing keywords, I would like to recommend my package Font Lock Studio. It's an interactive debugger for font-lock keywords, where you can step one part of the font-lock highlighting machinery at a time.