>>> d={'Adam':95,'Lisa':85}
>>> sum= 0.0
>>> for k,v in d.iteritems():
...     sum= sum + v
...     print k,':',v
... print 'average',':',sum / len(d)
  File "<stdin>", line 4
    print 'average',':',sum / len(d)
        ^
SyntaxError: invalid syntax
>>> d={'Adam':95,'Lisa':85}
>>> sum =0.0
>>> for k,v in d.iteritems():
...     sum=sum+v
...     print k,':',v
...
Lisa : 85
Adam : 95
>>> print 'average',':', sum /len(d)
average : 90.0

print 'average', ':', sum / len(d)  不是应该处于for循环内吗，退出for输入那sum的值不是0.0吗，0.0/len（d）不是0吗