BeautifulSoup ...不一致字段（可能存在或可能不存在）

Question

field_b可能存在或可能不存在。 print(field_b.text)导致

AttributeError: 'NoneType' object has no attribute 'text'

代码：

soup=BeautifulSoup(result, 'lxml')

for item in soup.find_all('li', class_='items'):
    field_a=item.find('span', class_='aaa')
    field_b=item.find('span', class_='bbb')
    field_c=item.find('span', class_='ccc')

    print(field_a.text,field_b.text,field_c.text)



result
------
<li class="items><span class="aaa">XXX</span><span class="bbb">XXX</span><span class="ccc">XXX</span></li>
<li class="items><span class="aaa">XXX</span><span class="ccc">XXX</span></li>
<li class="items><span class="aaa">XXX</span><span class="ccc">XXX</span></li>
<li class="items><span class="aaa">XXX</span><span class="bbb">XXX</span><span class="ccc">XXX</span></li>