[C++-sig] Private construction for python objects?

Stefan Seefeld seefeld at sympatico.ca
Fri Oct 24 21:34:13 CEST 2008

Robert Dailey wrote:
> Hi,
> I have a C++ class that I'm exposing to Python via the Boost.Python 
> library. This specific class is only created from C++. In other words, 
> it doesn't serve the user very much good to construct an instance of 
> this class from Python. A typical use case for obtaining an instance 
> of this class from python is as follows:
> import myCustomModule
> fooInstance = myCustomModule.GetFooInstance()
> However, I want to prevent the user from being able to do this:
> import myCustomModule
> fooInstance = myCustomModule.Foo()
> Let's assume the class in question with private construction is Foo. 
> The latter code snippet would be an example of the user directly 
> constructing an instance of Foo(). Is there a way to prevent this 
> through the BOOST_PYTHON_MODULE() definition? I'm not even really sure 
> if this can be done natively through Python. Thanks.

You can specify a 'noinit<>' argument to the class_<> constructor, 
indicating you don't want this to expose any constructor. Then, you may 
use make_constructor to provide your own custom construction (factory) 
function instead.

Please look for details in the online tutorial and reference manual, as 
well as the examples / tests that are part of the sources.



      ...ich hab' noch einen Koffer in Berlin...

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