Re: [C++-sig] test if object instance is instance of extension class in C++
Stefan,
many thanks, that of course did the trick. I'm not seeing the wood for the
trees
any more, I fear.
> > what's the recommended way to check if an object instance is an
instance of
> > my extension class
> > in C++ code?
> >
> > I'm currently doing a very ugly
> >
> > #define isMyExtensionClass(pyobj) (strcmp(pyobj->ob_type->tp_name,
> > "MyExtensionClass") == 0)
> >
> > on PyObj* pyobj.
> >
> > I bet there is a better way but just can't seem to find it.
>
> bpl::extract e(pyobj);
> if (e.check()) ...
>
> Note that you may want to use a reference type as template argument to
> the boost::python::extract type, if you want to retrieve the object by
> reference instead of by value.
>
> See http://www.boost.org/doc/libs/1_40_0/libs/python/doc/v2/extract.html
> for details.
Just for the record, this is what I do now:
inline
bool isMyExtensionClass(PyObject* &pyobj) {
bp::extract extractor(pyobj);
return extractor.check();
}
inline
bool isMyExtensionClass(bp::object &obj) {
bp::extract extractor(obj);
return extractor.check();
}
Thanks again & have a nice weekend
Holger
Landesbank Baden-Wuerttemberg
Anstalt des oeffentlichen Rechts
Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz
HRA 12704
Amtsgericht Stuttgart
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Re: [C++-sig] test if object instance is instance of extension class in C++
On 02/24/2012 05:44 AM, Holger Joukl wrote:
> Just for the record, this is what I do now:
>
> inline
> bool isMyExtensionClass(PyObject* &pyobj) {
> bp::extract extractor(pyobj);
> return extractor.check();
> }
I'm not sure why you use raw PyObject pointers in the first place. That
should all be hidden behind bpl::object instances (which will then take
care of the ref counting business for you).
> inline
> bool isMyExtensionClass(bp::object &obj) {
> bp::extract extractor(obj);
> return extractor.check();
> }
bp::object itself has reference (smart pointer) semantics, so there is
no need to pass objects by reference.
Stefan
--
...ich hab' noch einen Koffer in Berlin...
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Re: [C++-sig] test if object instance is instance of extension class in C++
Hi,
> On 02/24/2012 05:44 AM, Holger Joukl wrote:
> > Just for the record, this is what I do now:
> >
> > inline
> > bool isMyExtensionClass(PyObject* &pyobj) {
> > bp::extract extractor(pyobj);
> > return extractor.check();
> > }
>
> I'm not sure why you use raw PyObject pointers in the first place. That
> should all be hidden behind bpl::object instances (which will then take
> care of the ref counting business for you).
We're porting a legacy boost.python v1-wrapped library to current
boost.python.
Some parts of its internal methods operate on raw PyObject pointers. While
we're probably going to change that for now I all I want is a running
version
and change as little as possible.
> > inline
> > bool isMyExtensionClass(bp::object &obj) {
> > bp::extract extractor(obj);
> > return extractor.check();
> > }
>
> bp::object itself has reference (smart pointer) semantics, so there is
> no need to pass objects by reference.
I see. Just out of curiosity:
If I pass by reference I do save a copy constructor call, don't I?
But I circumvent the bp::object refcount safety, though(?).
But in a type check like above this shouldn't be dangerous - right?
Holger
Landesbank Baden-Wuerttemberg
Anstalt des oeffentlichen Rechts
Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz
HRA 12704
Amtsgericht Stuttgart
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Re: [C++-sig] test if object instance is instance of extension class in C++
On 02/24/2012 09:33 AM, Holger Joukl wrote: > bp::object itself has reference (smart pointer) semantics, so there is > no need to pass objects by reference. > I see. Just out of curiosity: > If I pass by reference I do save a copy constructor call, don't I? In principle, yes. I'm not sure how much of this the compiler would be able to optimize away, though. > But I circumvent the bp::object refcount safety, though(?). Well, yes, but you don't need that as C++ language semantics ensure the object lifetime. > But in a type check like above this shouldn't be dangerous - right? There is definitely no danger in doing this. It may just add a little bit of overhead (since in certain cases passing by value is cheaper than passing by reference, depending on the involved types and optimization level. Stefan -- ...ich hab' noch einen Koffer in Berlin... ___ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
Re: [C++-sig] test if object instance is instance of extension class in C++
> > bp::object itself has reference (smart pointer) semantics, so there is
> > no need to pass objects by reference.
> > I see. Just out of curiosity:
> > If I pass by reference I do save a copy constructor call, don't I?
>
> In principle, yes. I'm not sure how much of this the compiler would be
> able to optimize away, though.
>
> > But I circumvent the bp::object refcount safety, though(?).
>
> Well, yes, but you don't need that as C++ language semantics ensure the
> object lifetime.
>
> > But in a type check like above this shouldn't be dangerous - right?
>
> There is definitely no danger in doing this. It may just add a little
> bit of overhead (since in certain cases passing by value is cheaper than
> passing by reference, depending on the involved types and optimization
> level.
Ok, this sounds like its best to do
inline
bool isMyExtensionClass(PyObject* pyobj) {
bp::extract extractor(pyobj);
return extractor.check();
}
inline
bool isMyExtensionClass(bp::object obj) {
bp::extract extractor(obj);
return extractor.check();
}
Many thanks again Stefan,
Holger
Landesbank Baden-Wuerttemberg
Anstalt des oeffentlichen Rechts
Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz
HRA 12704
Amtsgericht Stuttgart
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Re: [C++-sig] how to override __setattr__ of an extension class
On 02/23/2012 12:04 PM, Holger Joukl wrote:
Hi,
I'm trying to instrument a wrapped class with custom __setattr__
mechanics:
.def("__setattr__",&MyExtensionClass::setattr)
How can I call the base class __setattr__ from within setattr and not run
into infinite recursion?
I.e. the analogon in C++ to
class Foo(object):
... def __setattr__(self, attr, value):
... print "custom __setattr__"
... object.__setattr__(self, attr, value)
...
foo = Foo()
foo.x = 23
custom __setattr__
foo.x
23
To actually write to my instance dict I currently do
PyObject* __dict__ = PyObject_GetAttrString(m_self, const_cast
("__dict__"));
PyDict_SetItemString(__dict__, name, value.ptr());
inside MyExtensionClass::setattr (where m_self is PyObj*)
Is there a better way?
Everything I can think of (e.g. extract the base class from __bases__[0]
and call its setattr) is functionally equivalent and not any prettier.
On a sidenote, I initially thought I could wrap the __dict__ in bp::dict()
to
use its nice Python-like API for item assignment but this seems to always
make a copy of the __dict__.
I.e something like
bp::dict bp_dict(__dict__);
bp_dict[name] = value;
won't work.
The trick is to do:
bp::dict bp_dict = bp::extract(__dict__);
bp_dict[name] = value;
Just calling the bp::dict invokes Python's dict constructor, which does
a copy.
Jim
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Re: [C++-sig] Wrapping a function that takes class type, such as type_info
On 02/24/2012 02:31 AM, Adam Preble wrote: Jim, I'll top post since I think this might get messy nice and fast otherwise. I found I couldn't get to a method wrapped to type a PyTypeObject* and only PyObject* would do. Yeah, that's not surprising. You can also have it take a boost::python::object; that's essentially a smart pointer for PyObject*. if(PyObject_IsInstance((PyObject*) internal_type, noIdea) == 1) I think this is the only line that needs to change; you just need to use PyObject_IsSubClass instead of PyObject_IsInstance. Right now you're asking whether "internal_type" is an instance of "noIdea", so the answer is only True when "noIdea" is "type". I think you want to ask whether "internal_type" is a subclass of "noIdea". And that's just: if (PyObject_IsInstance((PyObject*)internal_type, noIdea) == 1) Jim ___ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
