You can do this:
class MyElement(Element):
def is_regular(self):
from sage.my_parent import MyParent
P = MyParent()
That way you don't import MyParent when you import the element, only when
you run the is_regular() method.
Alternatively, the parent could have an is_regular(x) method and in the
element you just call self.parent().is_regular(self).
On Friday, November 9, 2012 2:36:23 PM UTC-5, Charles Bouillaguet wrote:
>
> On Nov 9, 2012, at 7:57 PM, Volker Braun wrote:
>
> > If you use the
> >
> > class MyParent(Parent)
> > Element = MyElement
> >
> > syntax then you have to import MyElement. So you shouldn't import
> MyParent in your element code or you will create a cyclic import (=bad).
> >
> > Are you sure that you need to create new parents from the element? Your
> element should only work with the parent that it is an element of. New
> Parents are generally constructed by coercion, but the coercion code lives
> in MyParent.
>
> It's a bit more complicated than that… The setting is that if R is a
> (multivariate) polynomial ring, and I is an ideal of R, then checking that
> elements of the quotient R/I are regular requires working with a new
> polynomial ring R', which is essentially a copy of R with one more
> variable.
>
> So, sage.rings.QuotientRingElement needs to create instances of
> multivariate polynomial rings.
>
> > If all fails you can still do a method-level import. But its likely that
> you should not.
>
> Sorry for not being very familiar with python, but could you elaborate a
> little?
>
> Thanks,
> Charles
>
> >
> >
> >
> >
> > On Friday, November 9, 2012 1:13:20 PM UTC-5, Charles Bouillaguet wrote:
> > Hi,
> >
> > Why does adding :
> >
> > from sage.rings.polynomial.polynomial_ring_constructor import
> PolynomialRing
> >
> > at the beginning of quotient_ring_element.py create the weird error:
> >
> > Traceback (most recent call last):
> > …
> > AttributeError: 'module' object has no attribute 'quotient_ring'
> >
> > Is there a circular dependency problem? If so, how can I possibly create
> polynomial rings inside quotient_ring_element ???
> >
> > Cheers,
> > ----
> > Charles Bouillaguet
> > http://www.lifl.fr/~bouillaguet/
> >
> > --
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> >
> >
>
>
>
> ---
> Charles Bouillaguet
> http://www.lifl.fr/~bouillaguet/
>
>
>
>
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