How to use the apiritif.random_string function in apiritif

def get_success_reader_alot(prefix='', offset=0):
    mock = MockReader()
    for x in range(2, 200):
        rnd = int(random() * x)
        mock.data.append((x + offset, prefix + random_string(1 + rnd), 1, r(), r(), r(), 200, '', '', 0))
    return mock

def get_fail_reader_alot(offset=0):
    mock = MockReader()
    for x in range(2, 200):
        rnd = int(random() * x)
        mock.data.append((x + offset, "first", 1, r(), r(), r(), 200, (random_string(1 + rnd)), '', 0))
    return mock

def random_url(target_len):
    base = 'http://site.com/?foo='
    return base + random_string(target_len - len(base))