you can do this
soup.findAll(True, {'class':['class1', 'class2']})
example:
>>> from bs4 import BeautifulSoup
>>> soup = BeautifulSoup('<html><body><div class="class1"></div><div class="class2"></div><div class="class3"></div></body></html>')
>>> soup.findAll(True, {"class":["class1", "class2"]})
[<div class="class1"></div>, <div class="class2"></div>]