python 中的 generator expression

看下面的代码

生成器不支持索引及切片。参看第4行。
生成器不支持与list相加。

如果需要生成器结果那么最好用list expression,

>>> def get_some_stuff():
... pass
...
>>> def gen():
... return(something for something in get_some_stuff())
...
>>> print gen()[:2]
Traceback (most recent call last):
  File "", line 1, in <module>
  File "", line 2, in gen
TypeError: 'NoneType' object is not iterable
>>> print [5,6]+gen()
Traceback (most recent call last):
  File "", line 1, in <module>
  File "", line 2, in gen
TypeError: 'NoneType' object is not iterable
>>>