How to register a built-in extension module?

[vadimcn]

I have a Rust app that hosts Python interpreter. I want to register a built-in module so that Python code can call back into the app.
Not sure how to convert #[pymodule] fn ..., into something I can give to PyImport_AppendInittab... Also, I need to support both Python 2 and 3, and it looks like I can't use wrap_pymodule! with Python2?

Would you mind providing an example?

[kngwyu]

I made it https://github.com/kngwyu/pyo3/blob/append-init-tab-example/examples/word-count/src/main.rs

But honestly I don't know when we should use PyImport_AppendInittab and feel this function difficult.
I also wrote an example of exposing function via locals(example2) and think it's enough for most cases.
Could you please let me know about your use case more concretely?

[konstin]

Sidenote: It's normally better to use PyModule::new() instead of make_module because make_module is not part of the public api (it's marked as #[doc(hidden)])

Also, I need to support both Python 2 and 3, and it looks like I can't use wrap_pymodule! with Python2?

Yes, wrap_pymodule! currently only supports python 3, because python 2 support would required some work on the python2 part which is going to be removed soon anyway.

[vadimcn]

@kngwyu: PyImport_AppendInittab is typically used when a module only makes sense in the context of an application (for example if Python is used for scripting application logic), so module code is linked statically to the main app binary.

The solution I can up with is this:

unsafe {
    #[cfg(Py_2)]
    let module_init = initmymodule;
    #[cfg(Py_3)]
    let module_init = PyInit_mymodule;
    pyo3::ffi::PyImport_AppendInittab("mymodule\0".as_ptr() as *const c_char, Some(module_init));
}

...but I was wondering if there's a more elegant way to do it..

because python 2 support would required some work on the python2 part which is going to be removed soon anyway.

I hope not before 1/1/2020?

[konstin]

I hope not before 1/1/2020?

No, definitely before. See https://python3statement.org/

[davidhewitt]

As there has been no discussion on this question for some time, I'm going to close it. Thank you for the discussion.