On Mar 13, 2011, at 13:09 , daveloeffler wrote:
> On Mar 13, 6:34 pm, "Justin C. Walker" <[email protected]> wrote:
>> Perhaps I should have expected this, but
>>
>> sage: R=Integers(5)
>> sage: L=R.list()
>> sage: L
>> [0, 1, 2, 3, 4]
>> ## I just want the *non-zero* elements:
>> sage: L.__delitem__(0)
>> sage: L
>> [1, 2, 3, 4]
>> ## Ah!
>> ## Uh-oh
>> sage: R.list()
>> [1, 2, 3, 4]
>> ## Better fix that...
>> sage: R=Integers(5)
>> ## Oops! I've broken Z/5*Z!!
>> sage: R.list()
>> [1, 2, 3, 4]
>
>>
>> I hope Sage isn't a distributed system, where the cache is shared across all
>> users...
>>
>> Is this a "Doctor: Then don't do that" moment, or should "obj.list()" return
>> a deep copy?
>
> Oh dear! The method "obj.list()" should *definitely* be returning a
> deep copy.
>
> Note that this is simultaneously revealing 2 bugs. The "broken" Z/5Z
> should go away when you re-create R, but it doesn't because there's a
> reference to it stored by the coercion model -- see #715.
The first is
<http://trac.sagemath.org/sage_trac/ticket/10927>
As for the second, I'm not sure. The cache issue is a side-effect of the bug,
no?
Once the bug is fixed (and you restart sage :-}), the second one shouldn't be a
problem.
>
>> ## But, ironically,
>> sage: R(0) in R
>> True
>
> (This is what you'd expect: containment checks don't construct a list
> first, since if they did, "3 in Integers(2^50)" would take rather a
> while...)
I'm guilty of over-ironizing (that was meant as a wise-crack (as of course is
this (...))).
Thanks!
Justin
--
Justin C. Walker, Curmudgeon at Large
Institute for the Absorption of Federal Funds
-----------
My wife 'n kids 'n dogs are gone,
I can't get Jesus on the phone,
But Ol' Milwaukee's Best is my best friend.
-----------
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