Trac WSGI script that sets database uri from environment variable

wsgi.py

import os
import trac.web.main
from trac.env import open_environment, Environment
from trac.util import translation
import gc
import threading

def application(environ, start_response):
    req = trac.web.main.RequestWithSession(environ, start_response)
    run_once = environ['wsgi.run_once']

    env = env_error = None
    try:
        env = Environment(os.environ['TRAC_ENV'])
        if env.base_url_for_redirect:
            environ['trac.base_url'] = env.base_url

        # Web front-end type and version information                                                                                                          
        if not hasattr(env, 'webfrontend'):
            mod_wsgi_version = environ.get('mod_wsgi.version')
            if mod_wsgi_version:
                mod_wsgi_version = (
                        "%s (WSGIProcessGroup %s WSGIApplicationGroup %s)" %
                        ('.'.join([str(x) for x in mod_wsgi_version]),
                         environ.get('mod_wsgi.process_group'),
                         environ.get('mod_wsgi.application_group') or
                         '%{GLOBAL}'))
                environ.update({
                    'trac.web.frontend': 'mod_wsgi',
                    'trac.web.version': mod_wsgi_version})
            env.webfrontend = environ.get('trac.web.frontend')
            if env.webfrontend:
                env.systeminfo.append((env.webfrontend,
                                       environ['trac.web.version']))
    except Exception, e:
        env_error = e

    print "Persistent database setting is %s" % env.config.get("trac", "database")
    if 'TRAC_DATABASE' in os.environ:
        env.config.set("trac", "database", os.environ['TRAC_DATABASE'])
    print "Overriding persistent database setting with %s" % env.config.get("trac", "database")

    translation.make_activable(lambda: req.locale, env.path if env else None)
    try:
        return trac.web.main._dispatch_request(req, env, env_error)
    finally:
        translation.deactivate()
        if env and not run_once:
            env.shutdown(threading._get_ident())
            unreachable = gc.collect()

I had to instantiate an Environment() directly instead of using open_environment() because the latter sets up a database connection in order to check if the environment needs to be upgraded .. so then it doesn't have any effect if I change the database config value after the connection has been opened.

But, this way the site will probably fail to check setup participants' environment_needs_upgrade functions .. so that probably needs to be added back in somewhere.