On Jun 2, 2008, at 10:18 PM, William Stein wrote:
> On Mon, Jun 2, 2008 at 10:15 PM, Robert Bradshaw
> <[EMAIL PROTECTED]> wrote:
>>
>> On Jun 2, 2008, at 9:51 PM, Igor Tolkov wrote:
>>
>>> I am trying to extend the integer class:
>>>
>>> {{
>>> class Quple(Integer):
>>> def __init__(self, a, b):
>>> Integer.__init__(self, b)
>>> self.tup = (a, b)
>>>
>>> print Quple(3,1)
>>> ///
>>>
>>> 0
>>> }}}
>>>
>>> I should get "1". I stared at this code for too long already.
>>
>> What are you trying to accomplish? In this case it could probably be
>> done an easier way because the Integer class has lots of hacks to
>> make it faster which may break extending it with a normal Python
>> class.
>>
>> - Robert
>
> Hi Robert,
>
> I just noticed this evil property of Sage integers, i.e., they are
> mutable
> no matter what:
>
> sage: n = 5
> sage: n.__init__(123)
> sage: n
> 123
>
> Abused this could easily lead to very subtle bugs, like the
> one below. Thoughts?
>
>
> sage: m = matrix(ZZ,2,[1,2,3,4])
> sage: d = m.det(); d
> -2
> sage: d.__init__(389)
> sage: m
>
> [1 2]
> [3 4]
> sage: m.det()
> 389
>
> The builtin Python integer type does *not* work this way:
>
> sage: n = int(5)
> sage: n.__init__(123)
> sage: n
> 5
>
> Bug?
Oh, that's bad... Of course, there's no stopping there:
sage: K.<a> = NumberField(x^2-2)
sage: a.__init__(K, 1/3)
sage: a
1/3
For Integers, I guess we could put more in the __new__ method, but I
think in general it's just something we're going to have to accept.
- Robert
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