Fixing integration with pytest-flake8

[VRGhost]

Hello,

The recent change to flake8's _stdoutWriteHook ( 7a353d2 ) breaks integration with some wrappers that attempt to capture flake8's sys.stdout output (e.g. pytest-flake8 does @ https://github.com/tholo/pytest-flake8/blob/master/pytest_flake8.py#L119 ), as it is uncommon for the capture code to emulate the .buffer attribute.

This PR modifies the stdout.write logic to be similar to sys.displayhook's ( https://docs.python.org/3/library/sys.html#displayhook ) that should keep everyone happy, hopefully - both Windows and integration people.

[asottile]

if you monkeypatch, that is at your own risk -- use io.TextIOWrapper instead

[RonnyPfannschmidt]

@asottile this is pytest output capture, i believe this should reopen /fix

[asottile]

@RonnyPfannschmidt it is not, pytest output capture does this correctly (I know because it was my first major contribution to pytest!)

def test():
    sys.stdout.buffer.write(b'hi\n')

[thijskramer]

But what (kind of) solution would both solve the problem that sys.stdout sometimes doesn't have a buffer attribute, and would be acceptable to you, @asottile ?

[RonnyPfannschmidt]

@asottile i see, ill crosscheck pytest flake8 once I recover from my cold as it seems to trigger this

[asottile]

sys.stdout always has the .buffer attribute unless it is poorly monkeypatched. as I said above, you probably want io.TextIOWrapper when replacing sys.stdout to properly match the real sys.stdout

[ptrcnull]

sys.stdout always has the .buffer attribute unless it is poorly monkeypatched. as I said above, you probably want io.TextIOWrapper when replacing sys.stdout to properly match the real sys.stdout

it is not "poorly monkeypatched" - even the official Python 3 documentation warns about this kind of situation:
https://docs.python.org/3/library/sys.html#sys.stdout

However, if you are writing a library (and do not control in which context its code will be executed), be aware that the standard streams may be replaced with file-like objects like io.StringIO which do not support the buffer attribute.

flake8 in this case should just check if sys.stdout has the buffer property and act accordingly..

[asottile]

the docs warn that people may do this wrong yes -- that doesn't mean we should support unsupported things