Find all attributes in an XML using Beautiful Soup

I have an XML file which looks something like this:

<tagA key1="val1" key2="val2" key3="val3">
<tagB.1 key1="val1" key2="val2" key3="val3"/>
<tagB.2 key1="val1" key2="val2" key3="val3"/>
<tagB.3 key1="val1" key2="val2" key3="val3"/>
<tagB.4 key1="val1" key2="val2" key3="val3"/>
<tagB.5 key1="val1" key2="val2" key3="val3"/>
</tagA>

What I am trying to do is extract the name of key1, key2 and key3 in tagB.x, and put them into a list. This way I can extract the values of it later. It should be able to handle more or less elements, being as each file is different. Thanks!