PyO3 Fails to Import DLL in Python Virtual Environment on Windows

Bug Description

When running cargo test within a python virtual environment on Windows, PyO3 fails to import DLLs, resulting in a STATUS_DLL_NOT_FOUND error. This occurs even after attempting to use --no-default-features to exclude potential issues caused by default feature sets.

Additional Attempt to Resolve:
Following the suggestion from the PyO3 FAQ, adding the directory containing the Python DLL (from the existing Python environment) to the PATH environment variable was attempted. However, this leads to importing modules from the existing Python environment instead of the virtual environment.

Steps to Reproduce

1. Set up a python virtual environment on Windows.

2. Create a minimal Rust project using PyO3.

3. Add a simple test case in src/lib.rs, for example:

    #[test]
    fn test() {
        pyo3::prepare_freethreaded_python();
        Python::with_gil(|py| {
            let _numpy = PyModule::import(py, "numpy").unwrap();
        });
    }

4. Run the project using cargo test.

5. Observe the error output.

Backtrace

No response

Your operating system and version

Win 10

Your Python version (python --version)

Python 3.11.0

Your Rust version (rustc --version)

rustc 1.71.0-nightly (4a59ba4d5 2023-05-12)

Your PyO3 version

0.19.2

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

python.org install
python -v venv venv

Additional Info

No response

Start with the minimal project and the test in src/lib.rs, then reproduce the failure by running cargo test on Windows inside a Python 3.11 virtual environment. Read the linked PyO3 FAQ guidance and compare DLL loading with and without the existing Python directory on PATH. Done means the test imports numpy from the virtual environment without STATUS_DLL_NOT_FOUND or selecting the wrong environment.