Re: [Boost-users] Exposing C++ Instances to Python

Subject: Re: [Boost-users] Exposing C++ Instances to Python
From: Leonhard Weber (lweberk_at_[hidden])
Date: 2010-05-25 11:34:17

Made a mistake... srry for my lacking knowledge/experience in C++. Trying to
improve :D.

For test purposes I changed the Python Script so it inits an instance, and
then tries to fetch the instance through the PyCallback:
#####
from EngineCallback import *

a = EngineCallback()
b = PyCallback(a)

>>> a
<EngineCallback.EngineCallback object at 0x7ffbe74c5208>
>>> b
<EngineCallback.EngineCallback object at 0x7ffbe74b0050>

#####
On the C++ side I had to change this, its now passing the argument by value
(which I dont want)
shared_ptr<EngineCallback> PyCallback( EngineCallback* test ) { return
shared_ptr<EngineCallback>(test); }

If I passed it per reference EngineCallback* &test (hope Im getting the
jargon right and not mixing up definitions) it would say:

did not match C++ signature:
    PyCallback(EngineCallback* {lvalue})

by changing it to pass by value it works, though isnt it making a copy of
the instance? how do I get just a reference to the instance passed to
Python?

On 25 May 2010 16:56, Steven Watanabe <watanabesj_at_[hidden]> wrote:

> AMDG
>
> Leonhard Weber wrote:
>
>> EngineCallback* test = new EngineCallback;
>>
>> // Entrypoint for Python to come ant fetch the Application Callback
>> shared_ptr<EngineCallback> PyCallback( EngineCallback* &test );
>> <snip>
>>
>> # test.py
>> from EngineCallback import PyCallback
>> from EngineCallback import EngineCallback
>>
>> test = PyCallback()
>>
>>
>
> PyCallback takes one argument.  Hence the exception below.
> Did you intend to use the global "test" instead of taking test
> as an argument in PyCallback?
>
>
>  Traceback (most recent call last):
>>  File "test.py", line 5, in <module>
>>    test = PyCallback()
>> Boost.Python.ArgumentError: Python argument types in
>>    EngineCallback.PyCallback()
>> did not match C++ signature:
>>    PyCallback(EngineCallback* {lvalue})
>>
>>
>
> In Christ,
> Steven Watanabe
>
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