revive a generator

[Yingjie Lan]

----- Original Message -----
> From: Paul Rudin <paul.nospam at rudin.co.uk>
> To: python-list at python.org
> Cc: 
> Sent: Thursday, October 20, 2011 10:28 PM
> Subject: Re: revive a generator
> 
> Yingjie Lan <lanyjie at yahoo.com> writes:
> 
>>  Hi,
>> 
>>  it seems a generator expression can be used only once:
>> 
>>>>>  g = (x*x for x in range(3))
>>>>>  for x in g: print x
>>  0
>>  1
>>  4
>>>>>  for x in g: print x #nothing printed
>>>>> 
>> 
>>  Is there any way to revive g here?
>> 
> 
> Generators are like that - you consume them until they run out of
> values. You could have done [x*x for x in range(3)] and then iterated
> over that list as many times as you wanted.
> 
> A generator doesn't have to remember all the values it generates so it
> can be more memory efficient that a list. Also it can, for example,
> generate an infinite sequence.
> 
> 
Thanks a lot to all who answered my question. 
I am still not sure why should we enforce that 
a generator can not be reused after an explicit 
request to revive it?