use low level apt_pkg cache to get list of upgradable packages (#68476)

prometheus-entrouvert-exporter/prometheus-system-exporter.py

@@ -9,7 +9,7 @@ import shlex
 import subprocess
 import time
 
-import apt
+import apt_pkg
 import dbus
 import psutil
 import requests
@@ -34,7 +34,6 @@ JOURNALD_IGNORED_ERRORS = {
 }
 
 
-apt_cache = apt.Cache()
 registry = CollectorRegistry()
 eo_errors = Gauge("eo_errors", "failed tests", ["ctn"], registry=registry)
 eo_certificates = Gauge("eo_certificates", "certificates", ["ctn", "name"], registry=registry)
@@ -157,9 +156,14 @@ def nginx(ctn):
 
 
 def packages(ctn):
+    apt_pkg.init()
+    cache = apt_pkg.Cache(None)
+    depcache = apt_pkg.DepCache(cache)
+    depcache.read_pinfile()
+    depcache.init()
     n = 0
-    for pkg in apt_cache.get_changes():
-        if pkg.isUpgradable:
+    for pkg in cache.packages:
+        if pkg.current_ver is not None and not depcache.marked_install(pkg) and depcache.is_upgradable(pkg):
             n += 1
     eo_packages.labels(ctn, "upgradable").set(n)