Unable to open file with long path on Windows

Bug Description

The behavior of pyo3 is inconsistent with the behavior of Python when opening files with extended paths over 256 characters long on Windows. When trying to execute the code via pyo3, it returns a FileNotFoundError. Long paths are enabled in the registry.

Steps to Reproduce

An example to reproduce the behavior, along with comparison to the python command follows. It requires python.exe to be accessible in PATH. If that's not the case, the PYTHON const should be updated to point to your python executable. The python command exits with code 0 (no exception), while the pyo3 part fails with FileNotFoundError.

src/main.rs

use pyo3::Python;
use std::ffi::CString;
use std::process::Command;

const PYTHON: &str = "python.exe";

fn main() {
    let tmpdir = tempfile::tempdir().unwrap();
    let mut pathbuf = tmpdir.path().to_path_buf();
    for i in 0..10 {
        pathbuf.push(i.to_string().repeat(30));
    }
    std::fs::create_dir_all(&pathbuf).unwrap();

    pathbuf.push("file.txt");
    std::fs::write(&pathbuf, "file contents").unwrap();

    assert!(pathbuf.as_path().as_os_str().len() > 256);

    let code = format!("open({:?})", pathbuf.to_str().unwrap());

    let cmd_result = Command::new(PYTHON)
        .args(["-c", &code])
        .spawn()
        .unwrap()
        .wait()
        .unwrap();

    let ccode = CString::new(code.as_str()).unwrap();
    let pyo3_result = Python::attach(|py| py.run(&ccode, None, None));

    println!(" cmd result: {cmd_result:?}");
    println!("pyo3 result: {pyo3_result:?}");
}
pyo3_result = Python::attach(|py| py.run(&ccode, None, None));

    println!(" cmd result: {cmd_result:?}");
    println!("pyo3 result: {pyo3_result:?}");
}

Cargo.toml

[package]
name = "pyo3_long_path_test"
version = "0.1.0"
edition = "2024"

[dependencies]
dirs = "6.0.0"
pyo3 = { version = "0.26.0", features = ["auto-initialize"] }
tempfile = "3.23.0"

Backtrace

Your operating system and version

Windows 11 Pro 23H2

Your Python version (python --version)

Python 3.13.1

Your Rust version (rustc --version)

rustc 1.90.0 (1159e78c4 2025-09-14)

Your PyO3 version

0.26.0

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

python.org installer

no virtualenv

Additional Info

No response

Start with the Windows reproduction in src/main.rs and its dependencies in Cargo.toml, then run it with Python 3.13 and PyO3 0.26 on Windows. Compare the embedded PyO3 result with the external Python command for a path longer than 256 characters; done means the embedded call opens the file without FileNotFoundError.