#19733: Assignment of special methods does not work in Cython
-------------------------------------+-------------------------------------
Reporter: jdemeyer | Owner:
Type: defect | Status: needs_review
Priority: blocker | Milestone: sage-6.10
Component: cython | Resolution:
Keywords: | Merged in:
Authors: Jeroen Demeyer | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jdemeyer/assignment_of_special_methods_does_not_work_in_cython|
fc92afbd3987de9790af923c2f5b97dc3e3da5f8
Dependencies: | Stopgaps:
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Description changed by jdemeyer:
Old description:
> In Cython, you cannot do
> {{{
> cdef class Foo:
> __str__ = whatever
> }}}
> and expect it to work.
>
> I don't know if this a Cython or Python bug or feature...
>
> -------
>
> When deriving a `class` (not `cdef class`) this kind of assignment
> suddenly works::
> {{{
> cdef class Base(object):
> def my_str(self):
> return "good"
> __str__ = my_str
>
> class Derived(Base):
> pass
> }}}
> gives
> {{{
> sage: str(Base())
> '<_home_jdemeyer__sage_temp_tamiyo_8430_tmp__MunIM_spyx_0.Base object
> at 0x7fb54ae544d0>'
> sage: str(Derived())
> 'good'
> }}}
>
> This also explains why the `__len__ = cardinality` in
> `src/sage/rings/finite_rings/finite_field_base.pyx` works. It doesn't
> work on the level of
> `sage.rings.finite_rings.finite_field_base.FiniteField`, but it works at
> the level of the actual finite field classes (which are Python classes).
New description:
In Cython, you cannot do
{{{
cdef class Foo:
__str__ = whatever
}}}
and expect it to work.
I don't know if this a Cython or Python bug or feature...
-------
When deriving a `class` (not `cdef class`) this kind of assignment
suddenly works::
{{{
cdef class Base(object):
def my_str(self):
return "good"
__str__ = my_str
class Derived(Base):
pass
}}}
gives
{{{
sage: str(Base())
'<_home_jdemeyer__sage_temp_tamiyo_8430_tmp__MunIM_spyx_0.Base object at
0x7fb54ae544d0>'
sage: str(Derived())
'good'
}}}
This also explains why the `__len__ = cardinality` in
`src/sage/rings/finite_rings/finite_field_base.pyx` works. It doesn't work
on the level of `sage.rings.finite_rings.finite_field_base.FiniteField`,
but it works at the level of the actual finite field classes (which are
Python classes).
--
--
Ticket URL: <http://trac.sagemath.org/ticket/19733#comment:7>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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