python 利用字典累加

aa=(1,2,3,42,4,5,4,3,2,56,33,56,56,34,33,43)
bb={}
for x in aa:
     try:
         bb[x]

     except:
         bb[x]=0
     finally:
         bb[x]=bb[x] + 1
print bb
for key in bb:
    print key,bb[key]