python3初学者，遇到一个关于print（）问题，请大家不吝赐教

>>> number_list = range(1, 11)
>>> number_filter = filter(lambda b:b%2==0, number_list)
>>> print(type(number_filter))
<class 'filter'>

class filter(object)

filter(function or None, iterable) –> filter object

Return an iterator yielding those items of iterable for which function(item) is true. If function is None, return the items that are true.

Python的迭代器协议使用的两个阶段

• 首先通过iter()调用设置并检索迭代器对象
• 然后通过next()反复从其获取值。

为了表示迭代结束，Python 迭代器只是引发了内置StopIteration异常，以表明没有更多的值可用于迭代。

>>> number_list = range(1, 11)
>>> number_filter = filter(lambda b:b%2==0, number_list)
>>> print(list(number_filter))    # list get all content of iterator
[2, 4, 6, 8, 10]
>>> next(number_filter)
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
StopIteration