Why do extension modules appear as members of themselves when imported?

[pydsigner]

This behavior shows up in my real projects and in a clean project using maturin init:

>>> import pyo3_test
>>> dir(pyo3_test)
['__all__', '__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__path__', '__spec__', 'pyo3_test', 'sum_as_string']

Why does pyo3_test show up as a member of the pyo3_test module?

>>> dir(pyo3_test.pyo3_test)
['__all__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'sum_as_string']

[ravenexp]

This happens because maturin creates a Python package containing an extension module with the same name, rather than a bare extension module.

pyo3_test.pyo3_test in your case refers to the inner extension module (the DSO/DLL binary built with rustc).

There are good reasons to use this layout, such as adding Python type stubs files (.pyi) to the package (see PEP 561).

[pydsigner]

Thanks, that's helpful! I might have been less confused if the _pyo3_test naming convention from C extension modules was used.