A bug due to copying a cython object.

[Kwankyu Lee]

Hi,

I observed

sage: F = GF(2)

sage: E = GF(4)

sage: phi = E.coerce_map_from(F); phi

Ring morphism:

  From: Finite Field of size 2

  To:   Finite Field in z2 of size 2^2

  Defn: 1 |--> 1

sage: phi.section()

---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)

...

TypeError: 'NoneType' object is not callable

and on the other hand,

sage: psi = E._internal_coerce_map_from(F)

sage: psi.section()

Section of (map internal to coercion system -- copy before use)

Ring morphism:

  From: Finite Field of size 2

  To:   Finite Field in z2 of size 2^2

If you look into coerce_map_from() method, essentially phi = copy(psi), but while copying the cython object, the information about the section map of psi is lost, and thus the error above.

What is the proper way to copy a cython object with all its attributes?

[Jeroen Demeyer]

On 2019-05-17 10:02, Kwankyu Lee wrote:
> What is the proper way to copy a cython object with all its attributes?

Write a __copy__ method doing the copy manually. Unless I'm missing a
Cython feature that helps with this.

[Kwankyu Lee]

This is now

https://trac.sagemath.org/ticket/27844

which needs review.