Use with open() as: to close file handles

[cclauss]

Like:

• test suite is keeping old filehandles around ardupilot#32533

% ruff rule SIM115

open-file-with-context-handler (SIM115)

Derived from the flake8-simplify linter.

What it does

Checks for cases where files are opened (e.g., using the builtin open() function)
without using a context manager.

Why is this bad?

If a file is opened without a context manager, it is not guaranteed that
the file will be closed (e.g., if an exception is raised), which can cause
resource leaks. The rule detects a wide array of IO calls where context managers
could be used, such as open, pathlib.Path(...).open(), tempfile.TemporaryFile()
ortarfile.TarFile(...).gzopen().

Example

file = open("foo.txt")
...
file.close()

Use instead:

with open("foo.txt") as file:
    ...

References

• Python documentation: open

[peterbarker]

I don't have a problem with adding SIM in. But the title on this PR is clear and the patches don't match it.

Please have your PRs do one thing and do it well.

[cclauss]

SIM and flake8 hate each other, so let's focus only on SIM115.

[peterbarker]

These patches all look correct.

How were they tested? We can not afford to break this stuff, and if it's wrong it's definitely going to break stuff.

[cclauss]

Can you please recommend a test plan?

In all cases, we read or write whole files in a single .read() or .write(), so there is only one command under the context manager and no intervening code to test between the open()/.read()/.close() or open/.write()/.close().

[cclauss]

@tpwrules Your review, please.

[peterbarker]

Can you please recommend a test plan?

Work out how to run each script so that the changes lines are crossed. Run the script. Make sure the script still does what it is supposed to do.

Incidentally, why are we not changing all of these to use pathlib.Path(...).read_text(encoding=utf8')?!