dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Oct 20, 2008 at 08:40:49AM +0200, Johan Hake wrote:
> On Sunday 19 October 2008 23:32:55 Martin Sandve Alnæs wrote:
> > 2008/10/19 Anders Logg <logg@xxxxxxxxx>:
> > > On Sun, Oct 19, 2008 at 09:04:17PM +0200, 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.
> > >
> > > ok.
> > >
> > >> 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 don't mind longer function names now that we don't use camelCaps
> > > anymore... :-)
> > >
> > > I'll wait for Martin's opinion.
> > >
> >
> > As Johan said, "a in b" or equivalently b.__contains__(a) is usually
> > taken to mean "a is an item in the container b". If type(b) is a
> > container type, it would be essential for __contains__ to have this
> > meaning, as it is a part of the "mapping protocol".
> >
> > However, since FunctionSpace is not a container type, overloading
> > FunctionSpace.__contains__(self, f) to mean "f in self" shouldn't pose
> > any problems that I see. There may exist python code in the world at
> > large that assumes an implementation of __contains__ means a container
> > type, but we don't need to interact with that code anyway.
> >
> > So I think we can safely e.g. rename "Function::in" to
> > "Function::in_space" in the swig interface, and then extend
> > FunctionSpace with an implementation of __contains__ like this:
> >
> >     def __contains__(self, f):
> >         return f.in_space(self)
> 
> Sounds resonable. 
> 
> Should I wait to send a patch for this untill we have renamed NewFunction to 
> Function? We need to change the python interface of Function any way when we 
> do the switch.
> 
> Johan

Sounds good.

-- 
Anders

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