>>> def I():
...     for i in range(10):
...             yield(i)
...
>>> iterobj = I()
>>> '1234567890'[:next(iterobj)]
''
>>> '1234567890'[:next(iterobj)]
'1'
>>> '1234567890'[:next(iterobj)]
'12'
>>> '1234567890'[:next(iterobj)]
'123'
>>> '1234567890'[:next(iterobj)]
'1234'
>>> '1234567890'[:next(iterobj)]
'12345'
>>> '1234567890'[:next(iterobj)]
'123456'
>>> '1234567890'[:next(iterobj)]
'1234567'
>>> '1234567890'[:next(iterobj)]
'12345678'
>>> '1234567890'[:next(iterobj)]
'123456789'
>>> '1234567890'[:next(iterobj)]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration