ImportError: dlopen(..., 0x0002): symbol not found in flat namespace _PyCMethod_New

[ghyatzo]

Hello,

I am having trouble manually building a python package. I developed it without issues using a virtual env and maturin develop, as in: it works and can be imported without issues.
Now, this library is the backbone of a python plugin and I need to vendor the library with the plugin itself.

I've followed the wiki about manual building thoroughly (at least i think) and I can cargo build without problems.
After copying the .dylib file into a properly renamed .so file I get the following error when importing:

>>> import my_lib_package
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dlopen(/correct/path/to/my/library/package/my_library_package.cpython-38-darwin.so, 0x0002): symbol not found in flat namespace '_PyCMethod_New'

Incidentally the very first line of my #[pymodule] function is a m.add_function call, If i comment it out the second line is a m.add_class::<>() call and the symbol not found becomes _PyObject_CallNoArgs.

I am a bit at a loss on what to do, has anybody have any idea what might be the issue or what I might be doing wrong?

Here is some context (if you need anything else let me know):
My Cargo.toml:

[package]
name = "MyLib"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
[lib]
name = "my_lib"
crate-type = ["cdylib"]

[dependencies]
mylib_in_rust = { path = "./ext/my_lib_in_rust" }
pyo3 = { version = "0.19", features = ["extension-module"] }
pyo3-asyncio = { version = "0.19", features = ["tokio-runtime"] }
tokio = "1.29.1"

[build-dependencies]
pyo3-build-config = "0.19.2"

Machine: M1 mac, Mac Os Ventura 13.1
Other Info: pyenv with only two versions: 3.8.10 (built with --enable-shared) and the system one.

[davidhewitt]

PyCMethod_New was added in Python 3.9 so you should check your build environment (you can do PYO3_PRINT_CONFIG=1 cargo build to get PyO3 to dump what it has detected). PyO3 has presumably detected a 3.9 interpreter (or newer) and is building with that one.

This is why it fails when you're importing on a 3.8 interpreter.

[ghyatzo]

Thanks a lot, I wrongly assumed that if building in a folder with a .python-version file pyo3 would use the local version set by pyenv.
Now with PYO3_PYTHON="$(pyenv which python)" cargo build it compiles and import correctly.

Strangely now, the lib works well when built with maturin while it acts up if manually built.
But that is probably on my end.

[TheGreekGod007]

dlopen(/Users/munzur/miniforge3/lib/python3.9/site-packages/scipy/spatial/_distance_wrap.cpython-39-darwin.so, 0x0002): symbol not found in flat namespace '_npy_copysign'