Gentoo: list optional dependencies for installed packages

optional_deps.py

#!/usr/bin/env python3

import re

import portage
import shlex

optfeature_re = re.compile(r'optfeature\s+(.*)$')

packages = portage.db[portage.root]['vartree'].dbapi.cpv_all()

for cpv in packages:
    ebuild = portage.db[portage.root]['vartree'].dbapi.findname(cpv)
    opts = []
    with open(ebuild) as fh:
        cont = False
        stack = []
        for line in fh:
            line = line.strip()
            if stack:
                if stack[-1][-1] == '\\':
                    stack.append(line)
                else:
                    full = ''.join(l.rstrip('\\') for l in stack)
                    a = shlex.split(full)
                    if a[0] != 'inherit':
                        opts.append(a)
                    stack = []
            else:
                m = optfeature_re.search(line)
                if m:
                    stack.append(line)
    if opts:
        print(cpv)
        for opt in opts:
            print('  ', opt)