On Mon, Jan 18, 2010 at 10:23:54AM -0800, Johan Hake wrote: > On Monday 18 January 2010 08:29:03 dbeacham wrote: > > New question #97842 on DOLFIN: > > https://answers.launchpad.net/dolfin/+question/97842 > > > > Is there a less hacked way to add extra parameter values to be used in an > > Expression in python than: > > > > class MyExp(Expression): > > def __new__(cls, *args, **kwargs): > > obj = Expression.__new__(cls, **kwargs) > > return obj > > > > def __init__(self, *args): > > .... > > .... > > It has been possible to pass user defined optional arguments to the __init__ > method. But it looks like a regression has kicked in. > > I have fixed the regression in dolfin dev, and added a doc string example. > > You should now be able to do: > > class MyExp(Expression): > def __init__(self, **kwargs): > self._mesh = kwargs['mesh'] > self._domain = kwargs['domain'] > def eval(self, values, x): > info(self._mesh, 1) > info(self._domain, 1) > > mesh = UnitCube(1,1,1) > domain = MeshFunction("uint", mesh, 0) > e = MyExp(mesh=mesh, domain=domain) > e(0,0,0) > > Do not use *args and do _not_ call the base class __init__. Yes, it is counter > intuitive but it is a result of having the Expression class do both compiled > Expressions and python derived Expressions. > > I prefer having two classes, CompiledExpression and Expression, so we could > say goodbye to this kind of troubles ;)
I'd prefer keeping "Expression" for the simplest option which is
visible in most demos:
f = Expression("sin(x[0])")
and find a suitable name for Expression with eval.
Ideally, it should also be the same in C++.
Candidates are
UserExpression
ComplexExpression
But I'm not sure I like any of them.
--
Anders
> Johan
>
>
> > where *args are my extra parameters (ie mesh, mesh functions etc.) and
> > __new__ might have to be better worked if I had included my own kwargs.
> > The above seems to work ok, but let me know of any major problems with it.
> >
> > I could always use a MyExp.init(...) function after I've created an
> > instance to set up class variables, but just curious as to whether I
> > missed something obvious for a one line initiation.
> >
> > David.
> >
>
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