#17953: inconsistency in returned type of BuiltinFunction result
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Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.6
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by rws:
Old description:
> It is generally preferred that the returned result type matches the
> argument type when calling a builtin function. For example this is as
> expected:
> {{{
> sage: factorial(8).parent()
> Integer Ring
> sage: factorial(SR(8)).parent()
> Symbolic Ring
> sage: exp(0).parent()
> Integer Ring
> sage: exp(SR(0)).parent()
> Symbolic Ring
> }}}
> but this is not:
> {{{
> sage: lambert_w(SR(0)).parent()
> Integer Ring
> }}}
>
> This ticket serves as a catch-all for such unexpected types.
New description:
It is generally preferred that the returned result type matches the
argument type when calling a builtin function. For example this is as
expected:
{{{
sage: factorial(8).parent()
Integer Ring
sage: factorial(SR(8)).parent()
Symbolic Ring
sage: exp(0).parent()
Integer Ring
sage: exp(SR(0)).parent()
Symbolic Ring
}}}
but this is not:
{{{
from sage.symbolic.function import BuiltinFunction
class TestFunction(BuiltinFunction):
def __init__(self):
BuiltinFunction.__init__(self, "testfun", nargs=2)
def _eval_(self, n, x, *args, **kwds):
print (parent(n), parent(x))
return SR(5)
sage: TestFunction()(SR(1),GF(2)(1))
(Integer Ring, Finite Field of size 2)
5
sage: type(_)
<type 'int'>
}}}
An explanation could be that `factorial` and `exp` derive from
`GinacFunction`.
--
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Ticket URL: <http://trac.sagemath.org/ticket/17953#comment:1>
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