Detect open() calls without with operator

[EugeneZelenko]

It'll be great to have check that will catch call to open() made without with operator. Probably check should work for other resource-allocating library calls.

[DudeNr33]

I'd be willing to work on this.
From what I've seen this would be a good addition to the existing RefactoringChecker in the form of a consider-using-with refactoring message.

@Pierre-Sassoulas let me know what you think.

[Pierre-Sassoulas]

Yes, nice refactoring message name :) ! I assigned you to the issue, thank you !

[benburk]

Thanks for the great addition! Unfortunately I'm not seeing it trigger on my end.

$ cat tmp.py
open('test.txt')


$ pylint tmp.py
************* Module tmp
tmp.py:1:0: C0304: Final newline missing (missing-final-newline)
tmp.py:1:0: C0114: Missing module docstring (missing-module-docstring)

----------------------------------------------------------------------
Your code has been rated at -10.00/10 (previous run: -10.00/10, +0.00)


$ pylint --version
pylint 2.8.2
astroid 2.5.6
Python 3.9.4 (default, Apr  9 2021, 09:32:38) 
[Clang 10.0.0 ]```

[DudeNr33]

That is because you did not assign the return value to anything.
Is this a legitimate use case for you?
I guess just the open call itself not, but you could do something like open("foo.txt", "w").write("hello world"). And in this case it would currently not trigger as well.

[EugeneZelenko]

But isn't file will not be closed in case of open("foo.txt", "w").write("hello world")'? So it'll be reasonable to extend check to cover such cases too.

[DudeNr33]

Yes, it would remain open.
I agree it would make sense, it just wasn't a use case I had in mind when implementing the check.

[hippo91]

@DudeNr33 should i reopen this issue?

[DudeNr33]

@hippo91 as this issue is already referenced as "closed" in previous release notes, I'd say no.
I will see what needs to be changed to detect the use case of open() outside an assignment, and if you prefer to have an issue to link the pull request against I can open a new one. Otherwise I'd just submit the PR.