Thank you, William. The __setitem__ emulation is definitely a better idea than the assign function, as the class is actually a container type.
But still I am looking for a way to allow the simple "data=42." syntax with the same result, because it would best copy the C++ syntax. Hans ----- Ursprüngliche Mail ---- > Von: William Ladwig <wlad...@wdtinc.com> > An: Development of Python/C++ integration <cplusplus-sig@python.org> > Gesendet: Montag, den 25. Mai 2009, 18:54:53 Uhr > Betreff: Re: [C++-sig] wrapping operator= > > Generally how that situation is handled on the Python side is to use the > container emulation API, so that assigning all values would look like this to > a > user of your class: > > data[:] = 42. > > To do this, you just need to write a small c++ wrapper to expose the > __setitem__(self, key, value) function, which accepts (or extracts) a slice > object for the key and then calls your class operator= function. Or, you > could > just stick with the assign function that you created, which may be better if > your class isn't supposed to look like a container. This may actually be > less > error prone. > > Here is the Python container emulation documentation: > > http://docs.python.org/reference/datamodel.html#emulating-container-types > > Other people may have better suggestions. > > Regards, > Bill > > ________________________________________ > From: cplusplus-sig-bounces+wladwig=wdtinc....@python.org > [cplusplus-sig-bounces+wladwig=wdtinc....@python.org] On Behalf Of Hans > Roessler > [hansroess...@yahoo.de] > Sent: Monday, May 25, 2009 9:08 AM > To: cplusplus-sig@python.org > Subject: [C++-sig] wrapping operator= > > Hello! > I want to wrap with boost.python a C++ class "DataCube" which has overloaded > the > operator=. > > The constructor DataCube::DataCube(double x) allocates huge amounts of > memory > and fills it with x's. > The DataCube::operator=(double x) just overwrites the already allocated > memory > with x's. > > Now in C++ these commands first allocate memory, which is filled with 0.'s, > and > then overwrite the memory with 42.'s: > >DataCube data(0.) > >data=42. > > In Python these commands first build the DataCube as desired, but then set > data=42. (now data is a float), where the reference to the DataCube is lost: > >data=DataCube(0.) > >data=42. > > I have circumvented this by replacing the second line with > > data.assign(42.) > with a function assign which is defined appropriately, but I would prefer to > use > the same assignment as in C++. > > Finally the question: > Can I define the DataCube class in Python, so that the data variable above > will > behave as in C++, when I write "data=42." ? > In other words, is there any possibility in Python that "x=y" does NOT make x > a > reference to y? > > Thank you > Hans > > > > > _______________________________________________ > Cplusplus-sig mailing list > Cplusplus-sig@python.org > http://mail.python.org/mailman/listinfo/cplusplus-sig > _______________________________________________ > Cplusplus-sig mailing list > Cplusplus-sig@python.org > http://mail.python.org/mailman/listinfo/cplusplus-sig _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
