Pyo3: SIGSEGV when PyIterator is given an integer

[althonos]

🐛 Bug Reports

PyIterator creates a SIGSEGV when passed an integer.

🌍 Environment

• Your operating system and version: Arch Linux 5.1.4-arch1-1-ARCH
• Your python version: 3.7.3
• How did you install python (e.g. apt or pyenv)? Did you use a virtualenv?: pacman -S python
• Your rust version (rustc --version): rustc 1.36.0-nightly (7158ed9cb 2019-05-15)
• Are you using the latest pyo3 version? Have you tried using latest master (replace version = "0.x.y" with git = "https://github.com/PyO3/pyo3")? yes, yes

💥 Reproducing

The following program will panic:

extern crate pyo3;

use pyo3::prelude::*;
use pyo3::types::PyIterator;

fn main() {
    let gil = Python::acquire_gil();
    let py = gil.python();

    let obj = 1.into_object(py);
    assert!(PyIterator::from_object(py, &obj).is_err());
}

with Cargo.toml:

[dependencies]
pyo3 = { git = "https://github.com/PyO3/pyo3" }

[birkenfeld]

This is because the return value from PyObject_GetIter in https://github.com/PyO3/pyo3/blob/master/src/types/iterator.rs#L42 is not checked for NULL.

I also don't understand why there is an additional PyIter_Check below (referring to #71)...