List and interactively purge all non-important APT packages.

do_purge.sh

#!/bin/bash

pkgs=$(./list_purgable.py)
for pkg in $pkgs; do
    echo "$(tput setaf 6)purging $pkg$(tput sgr0)"
    sudo apt purge "$pkg" || sudo apt-mark manual "$pkg"
done

list_purgable.py

#!/bin/python3

import apt

CACHE = apt.cache.Cache()
META_PKG_NAMES = ["desktop", "minimal", "server", "standard", "wsl"]
META_PKG_NAMES = ["ubuntu-" + x for x in META_PKG_NAMES]
IMPORTANT_PRIOS = ["required", "important"]


def is_important_pkg(pkg):
    return (pkg.essential or                                # essential
            (not pkg.is_auto_installed) or                  # installed manually
            (pkg.shortname in META_PKG_NAMES) or            # ubuntu meta package
            (pkg.installed.priority in IMPORTANT_PRIOS))    # prio = required or important


def add_recursive_dependencies(ver, deps):
    for dep in ver.dependencies:
        # if len(dep.installed_target_versions) > 1:
        #    print(f"NOTE: {dep} is satisfied by more than one package")

        dep_ver = dep.installed_target_versions[0]
        if not dep_ver in deps:
            deps += [dep_ver]
            add_recursive_dependencies(dep_ver, deps)


def print_pkg_list(pkgs):
    for pkg in pkgs:
        print(f"  - {pkg}")
    pass


# list installed important packages and their transitive dependencies
IMPORTANT_PKGS = []
IMPORTANT_PKGS_DEPS = []
for pkg in CACHE:
    # skip non-installed
    if pkg.installed is None:
        continue
    ver = pkg.installed

    # check whether important
    if is_important_pkg(pkg):
        IMPORTANT_PKGS += [ver]
        add_recursive_dependencies(ver, IMPORTANT_PKGS_DEPS)


# check each package if it could be purged
PURGES = []
for pkg in CACHE:
    # skip not installed packages
    if pkg.installed is None:
        continue
    pkg = pkg.installed

    # skip important packages
    if pkg in IMPORTANT_PKGS:
        continue

    # skip dependencies of important packages
    if pkg in IMPORTANT_PKGS_DEPS:
        continue

    PURGES += [pkg]

# print result
for pkg in PURGES:
    print(pkg.package.shortname)