#[pymodule(module="MODULE")] does not set the __module__ attribute

[amorenoz]

Bug Description

#[pyclass(module = "module")]
struct Foo {}

Correctly sets the __module__ attribute of the class.

The same behavior for other (sub) pymodules is expected.
The attribute is needed for tools such as https://github.com/mkdocstrings/griffe to properly find the submodule. See PyO3/maturin#1365.

What seems to happen is the module value of the submodule is used to determine the module value of the (inlined) pyclasses.

Steps to Reproduce

1. Create a module with a submodule. Use module="..."

/// Module documentation: A Python module implemented in Rust.
#[pymodule]
mod mymodule {
    use pyo3::prelude::*;

    /// Sub-Module documentation!!!
    #[pymodule(module="mymodule.mymodule.submodule")]
    mod submodule {
    	use super::*;

        #[pyclass]
        struct Foo{};

        /// Hack: workaround for https://github.com/PyO3/pyo3/issues/759   
        fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
            Python::with_gil(|py| {
                py.import("sys")?
                    .getattr("modules")?
                    .set_item("mymodule.submodule", m)
            })
        }
   }
}

2. Check the __module__ attribute`

>>> from mymodule import submodule
>>> submodule.__module__
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    submodule.__module__
AttributeError: module 'submodule' has no attribute '__module__'

Backtrace

Your operating system and version

Fedora 41

Your Python version (python --version)

Python 3.13.1

Your Rust version (rustc --version)

rustc 1.81.0 (eeb90cda1 2024-09-04)

Your PyO3 version

pyo3 v0.23.3 (https://github.com/PyO3/pyo3#5c363b5d)

How did you install python? Did you use a virtualenv?

dnf install python

Additional Info

As a workaround, __module__ attribute could be set manually:

        fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
            Python::with_gil(|py| {
                py.import("sys")?
                    .getattr("modules")?
                    .set_item("mymodule.submodule", m)
            })?;
            m.setattr("__module__", "mymodule.mymodule.submodule") // <-- Add this
        }

[amorenoz]

Sorry if this is the intended behavior, I might just be confused here.

Again, I just want griffe / mkdocs to generate documenation for me.

Interestingly, it seems that if a struct is embedded inside a module (not exported with #[pymodule_export], it's __module__ is, by default, the value you put into it's module's module="..." + the name of the module itself.

This is a bit confusing so I'll show code:

#[pymodule]
mod mymodule {
    use pyo3::prelude::*;

    #[pymodule(module="mymodule.mymodule")]
    mod submodule {
    	use super::*;

        #[pyclass]
        /// FooBar is also important
        struct FooBar {}

        /// Hack: workaround for https://github.com/PyO3/pyo3/issues/759
        #[pymodule_init]
        fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
            Python::with_gil(|py| {
                py.import("sys")?
                    .getattr("modules")?
                    .set_item("mymodule.submodule", m)
            })
        }
     }
}

results in:

>>> from mymodule import submodule
>>> submodule.FooBar.__module__
'mymodule.mymodule.submodule'
>>> 

Which is correct.

Now, for griffe to work, I need the module's __module__ to be mymodule.mymodule.submodule (as I posted here).

However, if I change it:

   #[pymodule(module="mymodule.mymodule.submodule")]
    mod submodule { ... }

griffe will still not work because:

>>> from mymodule import submodule
>>> submodule.__module__
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    submodule.__module__
AttributeError: module 'submodule' has no attribute '__module__'

But, the issue is now that:

>>> submodule.FooBar.__module__
'mymodule.mymodule.submodule.submodule'

I can fix griffe by manually setting the __module__ attribute but if this "bug" (I am not sure it one is now :-D) gets fixed I would have to manually set #[pyclass(module="mymodule.mymodule.submodule]" on FooBar.