pyd: implementing __hash__ and __str__ for PyD wrapped classes

[harfel via Digitalmars-d-learn]

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!