Speedup opportunity in install_remove.py

[Bob-A-Dook]

Hello :) I think I found an easy way to speed up opening the language pack window (in install_remove.py).

Currently, the cache object is refreshed twice when the MintLocale class is initialized. To illustrate:

class MintLocale:
    ...
    def __init__(self):
        ...
        self.cache = apt_pkg.Cache(None) #Updated
        ...
        self.build_lang_list()
        ...

    def build_lang_list(self):
        ...
        self.cache = apt_pkg.Cache(None) #Updated again

Each cache refresh is a heavy operation, taking around 0.4 seconds on my system (Mint 22.2, freshly loaded from a USB drive in live mode).

I think this can be easily improved by adding a refresh-controlling argument to build_lang_list. It could be false during initialization, but true in other cases (so that the cache stays up-to-date during future language list refreshes):

    def __init__(self):
        ...
        self.build_lang_list(refresh_cache=False)
        ...

    def build_lang_list(self, refresh_cache=True):
        ...
        if refresh_cache:
            self.cache = apt_pkg.Cache(None)

Ad-hoc benchmark

To check the speedup, I added some time measurements around the line where a MintLocale instance gets created.

from time import time

if __name__ == "__main__":
    t1 = time()
    MintLocale()
    t2 = time()
    print(t2-t1)
    Gtk.main()

Then I called the module directly (as root, so it gets access to system files):

sudo python3 /usr/lib/linuxmint/mintlocale/install_remove.py

Time before the change (2 refreshes):
1.2648556232452393

Time after the change (1 refresh):
0.7898681163787842

The effect should be noticeable to users who change language settings via the menu.