def get(self, id_or_url, default=None):
        """Fetch and return the spreadsheet with the given id or url.

        Args:
            id_or_url (str): unique alphanumeric id or URL of the spreadsheet
        Returns:
            New SpreadSheet instance or given default if none is found
        Raises:
            ValueError: if an URL is given from which no id could be extracted
        """
        if '/' in id_or_url:
            id = urls.SheetUrl.from_string(id_or_url).id
        else:
            id = id_or_url
        try:
            return self[id]
        except KeyError:
            return default