Ubuntu: Show version by version comparison of manually installed packages in current distribution with another distribution

pkg-diff.py

#!/usr/bin/env python
""" Show the difference between the versions of manually installed
packages on this system with the given distribution.
"""
import re
import sys

def main():
    if not distribution():
        sys.stderr.write("Could not determine distribution from /etc/os-release\n")
        sys.exit(-1)

    # Downloaded from http://packages.ubuntu.com/precise/allpackages?format=txt.gz
    my_packages = packages_for('precise.txt')
    # Downloaded from http://packages.ubuntu.com/trusty/allpackages?format=txt.gz
    upgrade_packages = packages_for('trusty.txt')

    for name in manually_installed():
        print '{: <30}{: <35} {}'.format(
            name,
            my_packages.get(name, 'NOTPRESENT'),
            upgrade_packages.get(name, 'NOTPRESENT'))

def packages_for(fname):
    with open(fname) as fd:
        [next(fd) for _ in range(6)]
        pkg = {}
        for line in fd:
            if 'virtual package provided by' in line:
                continue
            m = re.match(r"^(\S+) \(([^\s\)]+)", line)
            if not m:
                print 'Could not match on line %r' % line
                sys.exit(1)
            name, ver = m.groups()
            pkg[name] = ver
        return pkg

def manually_installed():
    # Create with  comm -23 <(aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)
    # http://askubuntu.com/questions/2389/generating-list-of-manually-installed-packages-and-querying-individual-packages
    with open('manually-installed.txt') as fd:
        return [s.strip() for s in fd]

def distribution():
    with open("/etc/os-release") as fd:
        for line in fd:
            m = re.match('VERSION=".+?, (\S+)', line)
            if m:
                return m.groups()[0].lower()

main()