Display text from img alt tag with beautifulsoup

So far my code is:

year = range(1958,2013)
randomYear = random.choice(year)
randomYear = str(randomYear)
page = range(1,5)
randomPage = random.choice(page)
randomPage = str(randomPage)
print(randomPage, randomYear)
url = 'http://www.billboard.com/artists/top-100/'+randomYear+'?page='+randomPage
url1 = urlopen(url)
htmlSource = url1.read()
url1.close()
soup = BeautifulSoup(htmlSource)
listm = soup.findAll('article', {'class': 'masonry-brick','style' : 'position;  absolute; top; 0px; left: 0px;'})
for listm in soup.findAll('div',{'class': 'thumbnail'}):
    for listm in soup.find('img alt')(''):
        print(listm)

What I want to do is get the img alt='' text. I think I have it correct, somewhat but it displays nothing.