>>> S='spam'
>>> E=enumerate(S)
>>> E
<enumerate object at 0x0000023AA0A91778>
>>> next(E)
(0, 's')
>>> next(E)
(1, 'p')
>>> next(E)
(2, 'a')
>>> next(E)
(3, 'm')
>>> next(E)
Traceback (most recent call last):
File "<pyshell#7>", line 1, in <module>
next(E)
StopIteration
>>>
>>> [c*i for (i,c)in enumerate(S)]
['', 'p', 'aa', 'mmm']
