set and dict iteration

[Hans Mulder]

On 8/09/12 22:06:08, Thomas Rachel wrote:
> Am 19.08.2012 00:14 schrieb MRAB:
> 
>>> Can someone who is more familiar with the cycle detector and cycle
>>> breaker, help prove or disprove the above?
>>>
>> In simple terms, when you create an immutable object it can contain
>> only references to pre-existing objects, but in order to create a cycle
>> you need to make an object refer to another which is created later, so
>> it's not possible to create a cycle out of immutable objects.
> 
> Yes, but if I add a list in-between, I can create a refcycle:
> 
> a = []
> b = (a,)
> a.append(b)
> 
> So b is a tuple consisting of one list which in turn contains b.
> 
> It is not a direct cycle, but an indirect one.

It's a cycle and it contains an immutable object, but it's not
a cycle consisting of immutable objects only.

As MRAB was arguing: it is not possbible to create a cycle
consisting of immutable objects only (unless you do unspeakable
things at the C level).

-- HansM