Bug Description

Getting an unexpected TypeError with strange message when converting Rust's FromUtf8Error to Python's UnicodeDecodeError. Not sure if other error/exception types are also affected, I haven't had a chance to check more thoroughly.

Steps to Reproduce

Using a simple function to create a Rust FromUtf8Error:

#[pyfunction]
fn unicode_error() -> PyResult<String> {
    Ok(String::from_utf8(b"\xff".to_vec())?)
}

From Python:

>>> unicode_error()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: function takes exactly 5 arguments (1 given)
Normalization failed: type=UnicodeDecodeError args='invalid utf-8 sequence of 1 bytes from index 0'
>>>

I expected to get the UnicodeDecodeError, instead getting a message (presumably) about PyO3 failing to construct the UnicodeDecodeError.

Backtrace

Your operating system and version

Ubuntu 24.04

Your Python version (python --version)

Python 3.12.3

Your Rust version (rustc --version)

rustc 1.89.0 (29483883e 2025-08-04)

Your PyO3 version

0.27.1

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

Installed Python through apt

Using a virtualenv and Maturin

Additional Info

No response