how to obtain the text for BeautifulSoup object

Mon Mar 19 20:59:05 EDT 2018

 Hi Team,
could anyone help me?
for webpage having source code like this:
...
<span class="xst thread-name">
 <em>number</em>
 <a class="xst">name</a>
</span>
I only can use below sentence, since there are a lot of tag em and tag a in
other area.
output = bs4.BeautifulSoup(res.content,'lxml').findAll("span",{"class":"xst
thread-name"})
how can I get the text in tag em and tag a under tag span?
thank you for your support!
Nathan