在 Word Reference 网站应该找不出反例，但 urljoin() 的第一个参数最好是当前地址，这样处理相对地址时才不会出错。下面是一个极端反例：
base = 'https://www.wordreference.com/definition/'
url = 'https://www.wordreference.com/definition/abc/123'
result1 = urljoin(url, 'def')
# result1 = 'https://www.wordreference.com/definition/abc/def'
result2 = urljoin(base, 'def')
# result2 = 'https://www.wordreference.com/definition/def'