Resolving TypeError in cppyy: Efficiently Using destroyModel in Python

In this post, we'll explore how to resolve the TypeError encountered when invoking `destroyModel` from a C+ + library using cppyy in Python and offer a practical workaround for efficient integration.
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Resolving TypeError in cppyy: Efficiently Using destroyModel in Python

When working with C+ + libraries in Python using cppyy, developers can sometimes encounter frustrating errors. One such issue arises when invoking destructor functions, like destroyModel, which require specific argument types. Today, we will address the common error message:

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Understanding the Problem

In the context of this issue, you are attempting to call the destroyModel function defined in a C+ + header file, which looks like this:

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You successfully called the functions createModel and process, but you faced difficulties with destroyModel. This function accepts a reference to a pointer (MYMODEL*& model), leading to the TypeError when calling it from Python.

The Root Cause

The primary issue stems from how cppyy handles pointers and references in C+ + . In this specific case, the argument passed to destroyModel does not match the expected type due to differences in how Python and C+ + represent pointers and references. Thus, when Python attempts to convert the argument, it fails, and the error arises.

The Solution

Fortunately, there is a straightforward workaround. Here’s how to properly pass the model pointer back for destroyModel using a simple struct definition.

Step-by-Step Workaround

Define a Fake Struct: To bypass the type conversion issue, you will define a simple struct in C+ + that acts as a placeholder for your model.

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Example Code

Here’s how the complete code should look after implementing the workaround:

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Conclusion

By utilizing a simple struct and the cppyy binding mechanism, you can effectively resolve the type conversion issue when working with C+ + method calls in Python. This workaround not only allows you to maintain code functionality but also simplifies the integration between Python and C+ + .

With this method, you can proceed with your development without being hindered by the tricky aspects of type compatibility in cppyy. Happy coding!