The
find_all
function returns a collection of objects, so you need to iterate the collection before you can use an index. Something like:
divs = soup.find_all("div", {'class':'cell'})
for div in divs:
print(div['data'])
Or, if you are certain that the first one in the list is the one you want then:
print(soup.find_all("div", {'class':'cell'})[0]['data'])