print function does not work within rust

[lorencarvalho]

🌍 Environment

• Your operating system and version: macOS Mojave 10.14.6 (18G95)
• Your python version: 3.7.4
• How did you install python (e.g. apt or pyenv)? macOS installer via python.org
• Did you use a virtualenv?: No, n/a as I'm calling Python from Rust.
• Your rust version (rustc --version): rustc 1.39.0-nightly (17e73e801 2019-08-28)
• Are you using the latest pyo3 version? Yes
• Have you tried using latest master (replace version = "0.x.y" with git = "https://github.com/PyO3/pyo3")? yes

💥 Reproducing

use pyo3::prelude::*;
use pyo3::types::PyDict;

fn main() {
    let gil = Python::acquire_gil();
    let py = gil.python();
    let locals = PyDict::new(py);
    py.run("foo = 'one'; print(foo)", None, Some(locals));
    py.run("print(\"hello python\"", None, None);
    println!("hello {}", locals.get_item("foo").unwrap());
}

Hello! It seems that calling print() in a Python snippet from within Rust does not work. I thought that perhaps Pyo3 did something with stdout/stderr file descriptors, but calling import code; code.interact() via a py_run! macro (surprisingly) does work, and everything seems mostly normal (save for sys.argv being an empty list and a few other expected oddities).

Obviously this isn't super high priority, but I figured I'd mention it :)

Thanks for such a cool project! Really excited to work with it.

[programmerjake]

    py.run("print(\"hello python\"", None, None);

you're missing the closing parenthesis ) in the print function call.

didn't test if that fixes it.

[lorencarvalho]

@programmerjake it doesn't, I just bungled copying my example code

[ehiggs]

It works here.
Ubuntu 19.10, python3 installed using apt. No venv. Rust 1.40 nightly 2019-11-7. pyo3 0.8.2.

$ python3 --version
Python 3.7.5rc1

$ cat src/main.rs 
use pyo3::prelude::*;
use pyo3::types::PyDict;

fn main() {
    let gil = Python::acquire_gil();
    let py = gil.python();
    let locals = PyDict::new(py);
    py.run("foo = 'one'; print(foo)", None, Some(locals)).expect("smash");
    py.run("print(\"hello python\")", None, None).expect("bang");
    println!("hello {}", locals.get_item("foo").unwrap());
}

$ ./target/debug/pyo3-test 
one
hello python
hello one

[programmerjake]

maybe it would work by using print(..., flush=True)?

[davidhewitt]

I think this was probably resolved by #943, so I'm going to close. If anyone encounters this and can provide another repro let's reopen.