What happens when you 'break' a generator?

Terry Reedy tjreedy at udel.edu
Tue Jul 29 09:51:05 CEST 2014


On 7/29/2014 3:18 AM, Frank Millman wrote:
> Hi all
>
> Python 3.4.1
>
> Here is a simple generator -
>
> def test():
>      print('start')
>      for i in range(5):
>          yield i
>      print('done')
>
> x = test()
> for j in x:
>      print(j)
>
> As expected, the output is -
>
> start
> 0
> 1
> 2
> 3
> 4
> done
>
> Here I break the loop -
>
> x = test()
> for j in x:
>      print(j)
>      if j == 2:
>          break
>
> Now the output is -
>
> start
> 0
> 1
> 2
>
> 'done' does not appear, so the generator does not actually terminate. What
> happens to it?

It sits there waiting for you to ask for the next value. Add
for j in x: print(j)
to exhaust it.  Even then, it sits there until garbage collected.



-- 
Terry Jan Reedy




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