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!

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).

On Wednesday, 5 April 2017 at 11:39:47 UTC, Nicholas Wilson wrote:
> On Wednesday, 5 April 2017 at 09:31:09 UTC, harfel wrote:
>> Dear all,
>>
>> [...]
>>
>> 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. >> 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__.
>>
>> [...]
>
> 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).

Unfortunately, this does not seem to be the case, as my D classes do override
toHash and toString, but they are not called by the corresponding python classes.