What happens when you 'break' a generator?

Frank Millman frank at chagford.com
Tue Jul 29 09:18:42 CEST 2014


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?

My guess is that normal scoping rules apply. Using my example, the generator 
is referenced by 'x', so when 'x' goes out of scope, the generator is 
garbage collected, even though it never completed.

Is this correct?

Frank Millman






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