#20204: problems with constructing or converting to SymPy expressions
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Reporter: rws | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.1
Component: symbolics | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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In the Sympy-1.0 upgrade the `UndefinedFunction._sage_` method is patched
away to enable the important upgrade. This function was planned to resolve
part of #14723 but uncovers missing functionality in the coercion system,
and probably with symbolics. The following doctest in french_book fails if
`UndefinedFunction._sage_` is defined:
{{{
sage: from sympy import Function, Symbol
sage: u = Function('u'); n = Symbol('n', integer=True)
sage: f = u(n+2)-(3/2)*u(n+1)+(1/2)*u(n)
NotimplementedError
}}}
tscrim found the minimal cases:
> {{{
> sage: f = function('f')
> sage: x = var('x')
> sage: sympy.sympify(f(x), evaluate=False)
> f(x)
> sage: sympy.sympify(3*f(x), evaluate=False)
> AttributeError: 'Call' object has no attribute 'id'
> }}}
> However, we do seem to have our own troubles of constructing !SymPy
objects from symbolic expressions. All of these result in errors:
> {{{
> sage: f._sympy_()
> sage: f(x)._sympy_()
> sage: (f(x)+3)._sympy_()
> }}}
This means that Sympy-1.0 probably only uncovered already existing
problems in expression conversion. This ticket should remove the patch in
`build/pkgs/sympy` and resolve all mentioned problems.
See #20185 for all previous discussion on this.
--
Ticket URL: <http://trac.sagemath.org/ticket/20204>
Sage <http://www.sagemath.org>
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