Returns normalized url. If schema is not given, would fall
        to filesystem
        (``file:///``) schema.

def _get_url(self, url):
        """
        Returns normalized url. If schema is not given, would fall
        to filesystem
        (``file:///``) schema.
        """
        url = str(url)
        if url != 'default' and not '://' in url:
            url = "file:" + urllib.pathname2url(url)
        return url