TypeError: 'builtin_function_or_method' object is not iterable

for i,n in Counter(ass).items():
    print('the word is %r the counter is % d'%(i,n))

上面如果items少了括号，会出现什么错误呢？
如下：

Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    for i,n in ass.items:
TypeError: 'builtin_function_or_method' object is not iterable

这是什么意思呢？