pyd: implementing __hash__ and __str__ for PyD wrapped classes

[Nicholas Wilson via Digitalmars-d-learn]

On Wednesday, 5 April 2017 at 09:31:09 UTC, harfel wrote:
> Dear all,
>
> Relatively new to D in general and PyD in particular, I am 
> trying to wrap some D classes I wrote for use in Python.
>
> Following the documentation and code examples, I got the basic 
> functionality working. However, I am struggling with 
> implementing the magic functions __str__ and __hash__ of the 
> extension class. My current approach was to implement them as 
> ordinary member functions:
>
>
> extern(C) void PydMain() {
> 	module_init();
>
> 	// Reaction
> 	wrap_class!(PyReaction,
> 		PyName!"Reaction",
> 		Init!(MultiSet, MultiSet),
> 		Property!(PyReaction.reactants),
> 		Property!(PyReaction.products),
> 		Repr!(PyReaction.repr),
> 		Def!(PyReaction.py_str, PyName!"__str__"),   // XXX needs slot
> 		Def!(PyReaction.py_hash, PyName!"__hash__"), // XXX needs slot
> 	)();
> }
>
> but this does not work. In Python:
>
> Python 2.7.12+ (default, Sep 17 2016, 12:08:02)
> [GCC 6.2.0 20160914] on linux2
> Type "help", "copyright", "credits" or "license" for more 
> information.
>>>> from teest_module import *
>>>> r=Reaction({'a':1, 'b':1}, {'ab':1})
>>>> r.__hash__
> <built-in method __hash__ of stochcalc.Reaction object at 
> 0x7fc1c7f4a080>
>>>> r.__hash__()
> 1430289695L
>>>> hash(r)
> 8779391257096
>
> According to related post for C++/SWIG 
> (http://stackoverflow.com/questions/25199233/str-not-called-when-printing-c-class-wrapped-for-python-with-swig), the reason is that these magic methods need to be implemented as slots, rather than ordinary member functions.
>
> Is there a way to declare these slots in PyD? I noticed that 
> Repr does this for __repr__ and the operator overloads do this 
> of course for their respective slots, but I could not find 
> anything for __hash__ and __str__.
>
> Any ideas?
>
> Thanks!

I haven't chased the source but most likely __hash__ and __str__ 
will be "magically" generated from toHash() and toString() 
respectively (both methods of Object, 
see:https://dlang.org/phobos/object.html#.Object).