Pytest reevaluates walrus operations within assert statements

[regananalytics]

• [x] a detailed description of the bug or problem you are having
• [x] output of pip list from the virtual environment you are using
• [x] pytest and operating system versions
• [x] minimal example if possible

Ubuntu 22.04, pytest 7.3.2, python 3.10.11

Package Version

---

exceptiongroup 1.1.1 iniconfig 2.0.0 packaging 23.1 pip 23.1.2 pluggy 1.0.0 pytest 7.3.2 setuptools 67.8.0 tomli 2.0.1 wheel 0.38.4

Pytest 7.3.2 re-evaluates walrus operator statements if they appear in assert statements.

def test_walrus():
    assert (x := 2) == 2
    x  =  3
    assert x == 3, "This test fails because (x := 2) is reevaluated by pytest"
    
def test_walrus_no_assert():
    (x := 2) == 2
    x = 3
    assert x == 3, "This test passes because (x := 2) is not reevaluated"

[The-Compiler]

Bisected to 331bc1be4634cf95fdb33021d4355c35723b73fe:

• #11041

As a workaround, --assert=plain works.

cc @aless10

[aless10]

Oh no! I'm thinking that a lot of edge cases are really really "edge", and I hope that nobody writes tests like this one. But I'm going to look at this. Is that ok with you? Thanks

[regananalytics]

Yeah, this is obviously not a real test. I wrote it as a super simple and replicable example of the issue.

[The-Compiler]

@aless10 Sure, please go ahead! No worries, sometimes things can be unexpectedly tricky. It's much appreciated that you're taking care of those follow-up issues!

[AdamVerner]

Just came across this issue as well when using pytest = "^8.3.3" Took me couple of hours to find out what is going on...