LooseVersion

t.py

import re
import apt
from json import dumps
from distutils.version import LooseVersion


def cmp_to_key(mycmp):
    'Convert a cmp= function into a key= function'
    class K:
        def __init__(self, obj, *args):
            self.obj = obj
        def __lt__(self, other):
            return mycmp(self.obj, other.obj) < 0
        def __gt__(self, other):
            return mycmp(self.obj, other.obj) > 0
        def __eq__(self, other):
            return mycmp(self.obj, other.obj) == 0
        def __le__(self, other):
            return mycmp(self.obj, other.obj) <= 0
        def __ge__(self, other):
            return mycmp(self.obj, other.obj) >= 0
        def __ne__(self, other):
            return mycmp(self.obj, other.obj) != 0
    return K


kernels = {}

# Regex for images
kernel_image_regex = '^linux-image-.*$'
kernel_header_regex = '^linux-(\w+-)?headers-.*$'
apt_cache = apt.Cache()

# Loop through all the packages
for pkg_name in apt_cache.keys():
    pkg = apt_cache[pkg_name]
    # Add to the kernels just installed and those in the kernel section
    if (pkg.is_installed
        and (
            ('kernel' in pkg.section
             and re.match(kernel_image_regex, pkg_name))
             or re.match(kernel_header_regex, pkg_name))):
        kernels.setdefault(pkg.installed.version, []).append(pkg.name)
# Print kernels, unsorted and sorted
print('Versions and packages:\n{}'.format(dumps(kernels, indent=4, sort_keys=True)))

kernel_versions = list(kernels.copy().keys())
print('Unsorted kernel/headers version:\n  {}'.format(kernel_versions))

try:
    sorted_kernel_list = sorted(kernel_versions, key=LooseVersion)
    print('Using LooseVersion:\n  {}'.format(sorted_kernel_list))
except TypeError:
    sorted_kernel_list = sorted(kernel_versions, key=cmp_to_key(apt.apt_pkg.version_compare))
    print('Using apt.apt_pkg.version:\n  {}'.format(sorted_kernel_list))

print('Reversed list using apt:\n  {}'.format(
    sorted(kernel_versions, key=cmp_to_key(apt.apt_pkg.version_compare), reverse=True)))