#15821: Change coercion to not use parent().an_element()
----------------------------+------------------------
Reporter: virmaux | Owner: virmaux
Type: defect | Status: new
Priority: major | Milestone: sage-6.2
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
The error traceback points to this code in
`sage.structure.parent.Parent._generic_convert_map`:
{{{
#!python
cpdef _generic_convert_map(self, S):
import coerce_maps
if self._convert_method_name is not None:
# handle methods like _integer_
if PY_TYPE_CHECK(S, type):
element_constructor = S
elif PY_TYPE_CHECK(S, Parent):
element_constructor = (<Parent>S)._element_constructor
if not PY_TYPE_CHECK(element_constructor, type):
# if element_constructor is not an actual class, get
the element class
element_constructor = type(S.an_element())
else:
element_constructor = None
if element_constructor is not None and
hasattr(element_constructor, self._convert_method_name):
return coerce_maps.NamedConvertMap(S, self,
self._convert_method_name)
...
}}}
So, this old code expects that `self._element_constructor` is a type, or
otherwise it tries to determine the type of an element.
Today, `_element_constructor_` rather than `_element_constructor` is used,
but it is not a type (it is a method).
And looking further down into the code, we find that the element
constructor actually is not really used: All what we do with it is to ask
{{{
hasattr(element_constructor, self._convert_method_name)
}}}
The point is: `self._convert_method_name` is None in our case! But if
there is no `_convert_method_name` then we really don't need the element
constructor (as a type) in the code.
Hence, my first guess is that we should first test whether
`self._convert_method_name` is None, and immediately skip that code block
if it is.
--
Ticket URL: <http://trac.sagemath.org/ticket/15821#comment:3>
Sage <http://www.sagemath.org>
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