apt-check.py

import sys
import apt_pkg

# init apt and config
apt_pkg.init()

# open the apt cache
try:
    cache = apt_pkg.Cache()
except SystemError, e:
    sys.stderr.write("Error: Opening the cache (%s)" % e)
    sys.exit(-1)

# setup a DepCache instance to interact with the repo
depcache = apt_pkg.DepCache(cache)

# take into account apt policies
depcache.read_pinfile()

# initialise it
depcache.init()

# give up if packages are broken
if depcache.broken_count > 0:
    sys.stderr.write("Error: Broken packages exist.")
    sys.exit(-1)

# mark possible packages
try:
    # run distro-upgrade
    depcache.upgrade(True)
    # reset if packages get marked as deleted -> we don't want to break anything
    if depcache.del_count > 0:
        depcache.init()

    # then a standard upgrade
    depcache.upgrade()
except SystemError, e:
    sys.stderr.write("Error: Couldn't mark the upgrade (%s)" % e)
    sys.exit(-1)

# run around the packages
upgrades = 0
for pkg in cache.packages:
    # skip packages not marked as upgraded/installed
    if not (depcache.marked_install(pkg) or depcache.marked_upgrade(pkg)):
        continue

    # increment the upgrade counter
    upgrades = upgrades + 1

print "Amount of upgrades: %d" % upgrades 

# return a count of possible packages
# or, maybe instead, collect a list of them to make it more useful