[Guidos Gorgeous Lasagna]: Tests Fail With Confusing pytest error if Student uses input()

[CodebyKhayla]

clicked "Run Tests" Got the following error:

We received the following error when we ran your code:
OSError: pytest: reading from stdin while output is captured! Consider using -s.

[BethanyG]

Hi @CodebyKhayla 👋🏽

Thank you for filing this issue! That is indeed concerning. I'm assuming that you tested your code via the website (please let me know if that's not the case). When I tried that exercise through the UI just now, I didn't receive that error - but that doesn't mean we don't have a problem.

Could you possibly provide the code you were testing, and any other details you can remember? That would be super helpful in tracking this down. Many thanks.

[CodebyKhayla]

Hi @BethanyG !

Wow, thanks for getting back to me so quickly. I definitely think my code is still not the right answer to the exercise, however, here is a screenshot.

[BethanyG]

Hi @CodebyKhayla

Your code does indeed have an issue. On line 9, you are defining a parameter that accepts interactive arguments from the command line (I am assuming as a test on your own system??). input() is something that you should in general be very cautious using. You must always intercept and check data from input(), as you cannot control what a user will type, and you must always sanitize anything before putting it to use in your program.

Our tests and testing framework are not designed for this sort of parameter, and (as you can see by the error thrown) pytest as we run it failed out because of the interactive prompt. All tests run in an isolated environment and that environment does not accept input from stdin or a command prompt.

We might examine blocking that feature of Python altogether in our test environment so that other users don't get confused by the pytest error. We don't have any exercises that deal with input(), and are not likely to add any in the near future.

Meanwhile, commenting out line 9 should get the tests to run for you. Let me know if that doesn't fix the problem.

[CodebyKhayla]

Thanks @BethanyG ! I definitely thought it was because of something I was doing.

Could it maybe be added to the instructions to not include input()?

Either way, thanks again, you've been amazing

[BethanyG]

Could it maybe be added to the instructions to not include input()?

🤔 As you have probably seen, the directions for this exercise are already quite long, and many students don't read them through to the end. Although maybe adding a comment in the stub to remind people could be a good addition. I will think about it.

We may need to just be up front with students and have a general doc that outlines the dos and don'ts of our online system. Neither input() nor print() generally work for any of our exercises (on the Python track at least). All of our exercises expect the use of return statements.

We will probably have exercises that do use print() in the future, but they will be purpose-built to have tests that check stdout, and are not on our immediate roadmap.

I'll keep this with a "bug" flag while I take a bit to think what we might want to do here. Thanks again for filing the issue -- and for providing the additional information!

[BethanyG]

Transferred issue here, because it most likely needs a solution in the runner.