def dispatch_request(environ, start_response):
    """Main entry point for the Trac web interface.

    :param environ: the WSGI environment dict
    :param start_response: the WSGI callback for starting the response
    """

    global _warn_setuptools
    if _warn_setuptools is False:
        _warn_setuptools = True
        warn_setuptools_issue(out=environ.get('wsgi.errors'))

    if sys.flags.optimize != 0:
        raise EnvironmentError("Python with optimizations is not supported.")

    # SCRIPT_URL is an Apache var containing the URL before URL rewriting
    # has been applied, so we can use it to reconstruct logical SCRIPT_NAME
    script_url = environ.get('SCRIPT_URL')
    if script_url is not None:
        path_info = environ.get('PATH_INFO')
        if not path_info:
            environ['SCRIPT_NAME'] = script_url
        else:
            # mod_wsgi squashes slashes in PATH_INFO (!)
            script_url = _slashes_re.sub('/', script_url)
            path_info = _slashes_re.sub('/', path_info)
            if script_url.endswith(path_info):
                environ['SCRIPT_NAME'] = script_url[:-len(path_info)]

    # If the expected configuration keys aren't found in the WSGI environment,
    # try looking them up in the process environment variables
    environ.setdefault('trac.env_path', os.getenv('TRAC_ENV'))
    environ.setdefault('trac.env_parent_dir',
                       os.getenv('TRAC_ENV_PARENT_DIR'))
    environ.setdefault('trac.env_index_template',
                       os.getenv('TRAC_ENV_INDEX_TEMPLATE'))
    environ.setdefault('trac.template_vars',
                       os.getenv('TRAC_TEMPLATE_VARS'))
    environ.setdefault('trac.locale', '')
    environ.setdefault('trac.base_url',
                       os.getenv('TRAC_BASE_URL'))


    locale.setlocale(locale.LC_ALL, environ['trac.locale'])

    # Determine the environment
    env_path = environ.get('trac.env_path')
    if not env_path:
        env_parent_dir = environ.get('trac.env_parent_dir')
        env_paths = environ.get('trac.env_paths')
        if env_parent_dir or env_paths:
            # The first component of the path is the base name of the
            # environment
            path_info = environ.get('PATH_INFO', '').lstrip('/').split('/')
            env_name = path_info.pop(0)

            if not env_name:
                # No specific environment requested, so render an environment
                # index page
                send_project_index(environ, start_response, env_parent_dir,
                                   env_paths)
                return []

            errmsg = None

            # To make the matching patterns of request handlers work, we append
            # the environment name to the `SCRIPT_NAME` variable, and keep only
            # the remaining path in the `PATH_INFO` variable.
            script_name = environ.get('SCRIPT_NAME', '')
            try:
                script_name = unicode(script_name, 'utf-8')
                # (as Href expects unicode parameters)
                environ['SCRIPT_NAME'] = Href(script_name)(env_name)
                environ['PATH_INFO'] = '/' + '/'.join(path_info)

                if env_parent_dir:
                    env_path = os.path.join(env_parent_dir, env_name)
                else:
                    env_path = get_environments(environ).get(env_name)

                if not env_path or not os.path.isdir(env_path):
                    errmsg = 'Environment not found'
            except UnicodeDecodeError:
                errmsg = script_name % 'Invalid URL encoding (was %r)'

            if errmsg:
                start_response('404 Not Found',
                               [('Content-Type', 'text/plain'),
                                ('Content-Length', str(len(errmsg)))])
                return [errmsg]

    if not env_path:
        raise EnvironmentError('The environment options "TRAC_ENV" or '
                               '"TRAC_ENV_PARENT_DIR" or the mod_python '
                               'options "TracEnv" or "TracEnvParentDir" are '
                               'missing. Trac requires one of these options '
                               'to locate the Trac environment(s).')
    run_once = environ['wsgi.run_once']

    env = env_error = None
    try:
        env = open_environment(env_path, use_cache=not run_once)
        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.webfrontend_version = environ['trac.web.version']
    except Exception as e:
        env_error = e

    req = RequestWithSession(environ, start_response)
    translation.make_activable(lambda: req.locale, env.path if env else None)
    try:
        return _dispatch_request(req, env, env_error)
    finally:
        translation.deactivate()
        if env and not run_once:
            env.shutdown(threading._get_ident())
            # Now it's a good time to do some clean-ups
            #
            # Note: enable the '##' lines as soon as there's a suspicion
            #       of memory leak due to uncollectable objects (typically
            #       objects with a __del__ method caught in a cycle)
            #
            ##gc.set_debug(gc.DEBUG_UNCOLLECTABLE)
            unreachable = gc.collect()
            ##env.log.debug("%d unreachable objects found.", unreachable)
            ##uncollectable = len(gc.garbage)
            ##if uncollectable:
            ##    del gc.garbage[:]
            ##    env.log.warn("%d uncollectable objects found.", uncollectable)
dataset/ETHPy150Open edgewall/trac/trac/web/main.py/dispatch_request/swapped operands of `%`