Re: Access to C++ dlls from Python

--- On Fri, 29/10/10, Diez B. Roggisch <[email protected]> wrote:

> Please reply to the mailing-list, not
> me personally.

Cheeky monkey!  You emailed *me* personally, so I replied 
personally. :-P

Further, some would consider it bad netiquette to forward a 
personal email to a public list, but never mind about that.

<snip>
> The compiler-question is potentially an issue if there is a
> mismatch  
> between the MSVCRT-variants Python and your DLL use, but
> that's a  
> problem under all circumstances.

You can see from my OP that I don't care.

> The discussions have taken place on this list, please
> google them. I  

I posted on the list because I couldn't find what I was looking
for using Google.   Search for what?  C++?  DLL?  Class?
Enlighten me please.

Most of the Googles I did on the subject ended up on posts where
someone asked similar questions, and got a barrage of replies 
ahem... explaining that they shouldn't do that.  Well, I want to 
do it, as they say in America 'get over it' :).  I see I've 
inadvertently now added to the list of 'non-answers' out there on 
the Interweb.  Sigh.... :(.

> can't comment on the state of affairs there, but in all
> honesty:  
> creating a patched + proprietary version of ctypes is *way*
> more  
> effort that to create C++ extension.

I wasn't really asking about which way is least effort, sorry if
you misunderstood.

> ctypes-C++ support would only be useful if it would work
> the same way  
> as ctypes does - seamless, without the need to invoke a
> compiler. It  

Here we agree.

> doesn't, and it seems to be a problem that's pretty hard.

I know nothing about ctypes-C++, but if it works by using a 
compiler, it's not what I'm after.

Hard?  Not for anyone doing any reverse-engineering of C++ code, 
so it seems.

> If you don't want to go down the C++-wrapper route, you
> might consider  
> wrtiting a simple C-API-wrapper that can be loaded using
> ctypes. That  
> however depends how high the trade-off between wrapping by
> hand and  
> generating is. The richer the C++-interface, the more you
> should check  
> out SIP.

Python is for many people a prototyping language.  It leads to 
other things.  This means once I've understood the principles 
in Python, I can then move on to similar implementations in 
other languages, including compiled ones.

I do not want to write a wrapper.  I want to use Python to 
interact at the ABI level.

I think all I need at the moment is a rather limited 
CALL_WITH_THIS(method, this, *args) type of function.

e.g.:

class MyVTable(Structure):
  _fields_ = [("Print", CFUNCTYPE(None, c_char_p))]

class MyClass(Structure):
  _fields_ = [("vtable", POINTER(MyVtable))]

dll = cdll.LoadLibrary("mydll.dll")
dll.GetObject.restype = POINTER(MyClass)
obj = dll.GetObject()
CALL_WITH_THIS(obj.contents.vtable.contents.Print, obj, "Hello World")

NB:  This might not even be valid ctypes code, I'm just typing it 
from memory, so don't pick it apart too much, just an example.

regards,
Biff.

> Diez





      

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