dolfin team mailing list archive

[Marie Rognes <meg@xxxxxxxxxxx>]

Johan Hake wrote:
> On Sunday 19 October 2008 00:24:36 Anders Logg wrote:
>   
> > On Sat, Oct 18, 2008 at 11:55:32PM +0200, Johan Hake wrote:
> >     
> > > On Saturday 18 October 2008 23:23:24 Anders Logg wrote:
> > >       
> > > > On Sat, Oct 18, 2008 at 10:16:32PM +0200, Johan Hake wrote:
> > > >         
> > > > > On Saturday 18 October 2008 21:24:53 Anders Logg wrote:
> > > > >           
> > > > > > On Thu, Oct 16, 2008 at 03:38:01PM +0200, Martin Sandve Alnæs wrote:
> > > > > >             
> > > > > > > "in" is a reserved keyword in python. Suggestions:
> > > > > > > "f.in_space(V)" or "f.in_function_space(V)" or "f.member(V)"
> > > > > > >               
> > > > > > How about keeping u.in(V) in C++ and then map it to something
> > > > > > suitable in Python so that one may write
> > > > > >
> > > > > >   if u in V:
> > > > > >       ...
> > > > > >
> > > > > > in Python. Does anyone know how to do that?
> > > > > >             
> > > > > There is a problem in the logic here. In c++ you ask the function if
> > > > > it is in a certain FunctionSpace, but the python code "u in V" would
> > > > > check if u is in V by calling V.__contains__(u). To make it more
> > > > > consistent we could implement the 'in' function in FunctionSpace, and
> > > > > then just rename 'in' to __contains__.
> > > > >
> > > > > You could also keep it the way it is and then rename Function.in to
> > > > > let say Function._in and then extend FunctionSpace with
> > > > >
> > > > >   def __contains__(self,u).
> > > > >       assert(u,Function)
> > > > >       return u._in(self)
> > > > >
> > > > > But then we would have different logics in c++ and python.
> > > > >
> > > > > Johan
> > > > >           
> > > > I think that would be ok, considering it is Python that maps "in" to
> > > > "contains". The logic and notation from a user perspective would be
> > > > the same in C++ and Python:
> > > >
> > > >   if (u.in(V))
> > > >   {
> > > >
> > > >   }
> > > >
> > > >   if u in V:
> > > >         
> > > I see your point and I agree.
> > >
> > > My logical error was attached to who implemented what. But to get the
> > > nice and from a user perspective logical syntax you present above, we
> > > need to implement it differently in c++ and python.
> > >       
> > ok, good. Can you implement it?
> >     
>
> Yes, but I would like to have Martins feedback on how 'pythonic' the 
> implementation is. 
>
> In most regards will the python version, "u in V" answer the question "is u an 
> item in V", where V is interpreted as a sequence or container. The function, 
> u is strictly speeking not an item in V. You can for example not access u 
> from V.
>
> It's just a gut feeling I have that we might stretch the python interface a 
> bit here. This is maybee not a bad idea when you have the somewhat 
> minimalistic function name 'in' from c++ in mind, but if you have a pure 
> python background it could be a bit confusing. 
>
> I think I would go for the _slightly_ more verbal u.in_space(V) 
> implementation. You should not avoid two word function name for all cost ;)
>
>   

I might be butting in here, but isn't the main idea of the special 
Python methods __contains etc,  precisely the possibility of decoupling 
the abstraction idea from the implementation?

Here, I imagine that the point is to represent a mathematical 
abstraction - whether a function is an element of a function space. In 
my opinion, the syntax

   if u in SpaceOfPiecewiseSomething:
        
does this well.

--
Marie E. Rognes
Ph.D Fellow, 
Centre of Mathematics for Applications, 
University of Oslo
http://folk.uio.no/meg