This checkin broke the buildbots.  If you build trunk then run

./python -bb -m test test_site

the test fails.  "-bb" is used by the normal test runner ("make test").

The problem is in the lines

        self.assertTrue(os.path.isabs(os__file__),
                        "expected absolute path, got {}".format(os__file__))
        self.assertTrue(os.path.isabs(os__cached__),
                        "expected absolute path, got {}".format(os__cached__))

os__file__ and os__cached__ are bytes but you're passing them into .format() on a str.