How to print stuff in a py.test finalizer

I'm testing a function that writes to a logfile (it doesn't matter that it writes to a logfile specifically, it could be doing anything, it's just what gave rise to this question)

Something like this:

def do_stuff():
    with open('/tmp/mylogs.txt', 'a') as f:
        f.write(str(time.time()))
        f.write(' stuff done! \n')
    return 42

And I can test it a bit like this:

def test_doing_stuff(watch_logs):
    assert do_stuff() == 42
    assert do_stuff() == 43

For debugging purposes, when a test fails, I want to be able to print out the new contens of the logs -- I can make a fixture a bit like this:

@pytest.fixture()
def watch_logs(request):
    with open('/tmp/mylogs.txt') as f:
        log_before = f.read()

    def get_new_logs():
        with open('/tmp/mylogs.txt') as f:
            log_after = f.read()
            return log_after.replace(log_before, '')

    return get_new_logs

Great - now I can check the log contents at any point in my tests:

def test_doing_stuff(watch_logs):
    assert do_stuff() == 42
    print(watch_logs())
    assert do_stuff() == 43
    print(watch_logs())

Hm - ah, but that second print isn't going to work, it's after the test failure.

What if my test fixture just always printed the logs out at the end of the test? Then pytest's stdout capture would show it to me when it fails, but not when it passes!

@pytest.fixture()
def watch_logs(request):
    with open('/tmp/mylogs.txt') as f:
        log_before = f.read()

    def get_new_logs():
        with open('/tmp/mylogs.txt') as f:
            log_after = f.read()
            return log_after.replace(log_before, '')

    def print_new_logs():
        print('~' * 20 + ' logs ' + '~' * 20)
        print(get_new_logs())
        print('~' * 50)
    request.addfinalizer(print_new_logs)

    return get_new_logs

Oh, but that doesn't work because pytests's log capture isn't happening during test finalizers.

So the question is: how can I make a test finalizer that can print stuff?