#12919: Typo in Parent.discover_coerce_map_from
-------------------------------------+--------------------------------------
Reporter: nthiery | Owner: robertwb
Type: defect | Status: positive_review
Priority: major | Milestone: sage-5.1
Component: coercion | Resolution:
Keywords: days38 | Work issues:
Report Upstream: N/A | Reviewers: André Apitzsch
Authors: Nicolas M. Thiéry | Merged in:
Dependencies: | Stopgaps:
-------------------------------------+--------------------------------------
Comment (by mguaypaq):
Here is a minimal example which illustrates the problem:
{{{
sage: class P(Parent):
....: def __init__(self):
....: Parent.__init__(self, category=Sets())
....: Element=ElementWrapper
....:
sage: A = P(); a = A('a')
sage: B = P(); b = B('b')
sage: C = P(); c = C('c')
sage: D = P(); d = D('d')
sage: Hom(A, B)(lambda x: b).register_as_coercion()
sage: Hom(B, A)(lambda x: a).register_as_coercion()
sage: Hom(C, B)(lambda x: b).register_as_coercion()
sage: Hom(D, C)(lambda x: c).register_as_coercion()
sage: A(d)
---------------------------------------------------------------------------
UnboundLocalError Traceback (most recent call
last)
/home/mguaypaq/<ipython console> in <module>()
/opt/sage-5.0.rc0/local/lib/python2.7/site-
packages/sage/structure/parent.so in sage.structure.parent.Parent.__call__
(sage/structure/parent.c:7906)()
/opt/sage-5.0.rc0/local/lib/python2.7/site-
packages/sage/structure/parent.so in
sage.structure.parent.Parent.convert_map_from
(sage/structure/parent.c:15248)()
/opt/sage-5.0.rc0/local/lib/python2.7/site-
packages/sage/structure/parent.so in
sage.structure.parent.Parent.discover_convert_map_from
(sage/structure/parent.c:15399)()
/opt/sage-5.0.rc0/local/lib/python2.7/site-
packages/sage/structure/parent.so in
sage.structure.parent.Parent.coerce_map_from
(sage/structure/parent.c:14021)()
/opt/sage-5.0.rc0/local/lib/python2.7/site-
packages/sage/structure/parent.so in
sage.structure.parent.Parent.discover_coerce_map_from
(sage/structure/parent.c:14958)()
/opt/sage-5.0.rc0/local/lib/python2.7/site-
packages/sage/structure/parent.so in
sage.structure.parent.Parent.coerce_map_from
(sage/structure/parent.c:14021)()
/opt/sage-5.0.rc0/local/lib/python2.7/site-
packages/sage/structure/parent.so in
sage.structure.parent.Parent.discover_coerce_map_from
(sage/structure/parent.c:14966)()
UnboundLocalError: local variable 'connecting' referenced before
assignment
}}}
With the patch, the output is now (as it should be):
{{{
sage: class P(Parent):
....: def __init__(self):
....: Parent.__init__(self, category=Sets())
....: Element=ElementWrapper
....:
sage: A = P(); a = A('a')
sage: B = P(); b = B('b')
sage: C = P(); c = C('c')
sage: D = P(); d = D('d')
sage: Hom(A, B)(lambda x: b).register_as_coercion()
sage: Hom(B, A)(lambda x: a).register_as_coercion()
sage: Hom(C, B)(lambda x: b).register_as_coercion()
sage: Hom(D, C)(lambda x: c).register_as_coercion()
sage: A(d)
'a'
}}}
This could be added as a doctest to detect the problem, but maybe it's not
necessary for such a clear typo. I would also note that
[http://trac.sagemath.org/sage_trac/ticket/7420#comment:3 this comment]
from #7420 points out a cleaner way to fix the problem, but this patch is
fine too.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12919#comment:9>
Sage <http://www.sagemath.org>
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