[Python-Dev] List mutation in list_repr?

[Serhiy Storchaka]

On 07.12.16 12:19, Patrick Westerhoff wrote:
> On Tue, Dec 6, 2016 at 5:32 PM, Random832 <random832 at fastmail.com> wrote:
>> It *shouldn't*, but it can't be enforced. It's one of those things where
>> if Python assumes all user code is sane (in this case, overridden
>> __repr__ not messing with the list) it can bite in a way that could
>> cause the interpreter to crash.
>
> I guess you are right. That makes sense. I didn’t think about the
> possibility that although the repr implementation is happening in
> native code where the user objects have no access to, the list object
> could still be referenced outside of the repr call.

There is another reason. Executing Python code can release GIL. The list 
object can be modified in other thread.