| msg123948 - (view) |
Author: Alexander Belopolsky (belopolsky) *  |
Date: 2010-12-14 14:53 |
| The work-around that I proposed for does not work with Python 2.x: $ python2.7 dict-graph.py Vertex 0 -> 2, 1 Vertex 1 -> Vertex 2 -> Traceback (most recent call last): File "dict-graph.py", line 74, in p = pickle.dumps(g) ... File ".../Lib/pickle.py", line 661, in _batch_setitems for k, v in items: RuntimeError: dictionary changed size during iteration |
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| msg180046 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2013-01-15 20:06 |
| It's interesting. The example behaves unstable on 3.3+ with C implementation of picle, sometimes works, sometimes fails. With Python implementation and on 3.2 it works always. On 2.7 it fails always. A difference between C and Python implementations of pickle is a bug and should be fixed. |
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| msg180048 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2013-01-15 20:16 |
| I find the posted code mystifying. As the name suggests, __getstate__ should probably not mutate anything. It would be nice if you could post a simpler example to reproduce issue. Even better if it doesn't have a mutating __getstate__, I would say. |
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| msg180088 - (view) |
Author: Charles-François Natali (neologix) * |
Date: 2013-01-16 13:07 |
| > It's interesting. The example behaves unstable on 3.3+ with C implementation of picle, sometimes works, sometimes fails. With Python implementation and on 3.2 it works always. On 2.7 it fails always. That's hash randomization. |
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| msg186882 - (view) |
Author: Alexandre Vassalotti (alexandre.vassalotti) * |
Date: 2013-04-14 05:03 |
| The mutating __getstate__ is very likely the problem here. I've attached a small test case which shows the described behavior. We could fix this by always making a copy of any mutable container we want to iterate over to save its items. Performance-wise this solution is not very attractive. We are better off documenting this behavior as a limitation of __getstate__. |
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| msg288262 - (view) |
Author: Raymond Hettinger (rhettinger) * |
Date: 2017-02-21 04:07 |
| I agree with Antoine that, "As the name suggests, __getstate__ should probably not mutate anything." Unless a problematic non-mutating example can be found, I suggest this be closed. For the most part, our rule has been that pure python code doesn't have to (and possibly cannot) defend itself against mid-stream mutation, while C code only has to defend itself to the point of avoiding a segfault. IMO, "RuntimeError: dictionary changed size during iteration" is an informative error message in this case. |
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