SIM115 false positive on functions that return file handler objects

[gboeing]

ruff 0.7 gives a false positive for SIM115 on something like:

def my_function(filepath, encoding):
    return bz2.open(filepath, mode="rt", encoding=encoding)

which can be resolved like:

def my_function(filepath, encoding):
    with bz2.open(filepath, mode="rt", encoding=encoding) as f:
        return f

But this prevents the calling function from being able to work with f because the context manager has closed it. It seems that SIM115 should not trigger when returning a file handler object from a function?

[zanieb]

Yeah strong agree that this should not be flagged.

Related #13679 (comment)

[AlexWaygood]

I agree that this could be improved. FWIW, though, this is really a pre-existing issue that could occur prior to Ruff 0.7. For example, Ruff 0.1 emits SIM115 on this code that uses the builtin open function:

def my_function(filepath, encoding):
    return open(filepath, mode="rt", encoding=encoding)

The only difference in Ruff 0.7 is that the rule is now applied consistently to more stdlib functions that open files, rather than just the builtin open function and pathlib.Path.open.

[AlexWaygood]

def my_function(filepath, encoding):
    return bz2.open(filepath, mode="rt", encoding=encoding)

Ideally, of course, rather than writing a wrapper function that returns an open file handle, you'd write a wrapper context manager that yields an open file handle, because then you can be confident that the file will always be closed after you're done with it:

from contextlib import contextmanager

@contextmanager
def my_function(filepath, encoding):
    with bz2.open(filepath, mode="rt", encoding=encoding) as f:
        yield f

Enforcing that kind of practice is probably outside the scope of this rule, however.