Problem with assigning variables of type List

Abhishek Roy abhishek at ocf.berkeley.edu
Wed Aug 21 21:02:54 CEST 2002


Peter Hansen <peter at engcorp.com> wrote in message news:<3D631501.3A308807 at engcorp.com>...
> Abhishek Roy wrote:
> > Just a nagging doubt, using the terminology in the above guide what's going
> > on with:
> > >>> a=[1,2,3]
> > >>> a[1]=a
> > >>> a
>  [1, [...], 3]
> > >>> a==a[1]
> > 1
> 
> You created a recursive object, which contains a reference to itself.
> Since this goes down infinitely deep, and you can't compare infinities,
> I thought, I wonder whether the "1" is mathematically true.  It is
> certain true according to Python's rules though.
I was just wondering how it's implemented. Since a[1]=a is really 
a.__setitem__(1,a), what exactly happens when you call this function
and then later make the comparison a==a[1]?

Abhishek



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