Append the string supplied to the log (a list of strings). If
        additional arguments are supplied, then first string is assumed to be
        a format string and the other args are used for string interpolation.
        For instance `backup.log("%d + %d == %d", 1, 1, 2)` would result in the
        string `'1 + 1 == 2'` being logged

def log(self, entry, *args):
        """Append the string supplied to the log (a list of strings). If
        additional arguments are supplied, then first string is assumed to be
        a format string and the other args are used for string interpolation.
        For instance `backup.log("%d + %d == %d", 1, 1, 2)` would result in the
        string `'1 + 1 == 2'` being logged"""
        if args:
            entry = entry % args
        self.backup_log.append(entry)