pytest 3.3.0 immutable fixture params

Before v3.3.0 it was possible to mutate fixture parameters, since v3.3.0 params gets “frozen” (I guess its introduced with this commit 07b2b18a01a3ba12757a4eb1c0e082922f5299e5)

I was using this feature to setup fixture parameters based on command-line options:

BINS = []

@pytest.fixture(scope='session', params=BINS, ids=...)
def server_bin(request):
    return request.param

@pytest.fixture(scope='session')
def run_server(server_bin):
    pass # start application

def pytest_configure(config):
    BINS[:] = config.getoption('--server')[:]

• Here is the real use case https://github.com/aio-libs/aioredis/blob/pyup/tests/conftest.py#L245-L254
• Here are the travis builds before and after update;

So my questions:

• Is this new behavior intended or its a bug?
• And if its intended what is new way to make dynamic parameters?

[nicoddemus]

@argaen and @popravich agree, thanks for the suggestion: #2980

[popravich]

@nicoddemus, the suggested code works with a tiny fix

def pytest_configure(config):
  class DynamicFixturePlugin(object):
     @pytest.fixture(scope='session', params=config.getoption('--servers'), ids=...)
-     def server_bin(request):
+     def server_bin(self, request):
        return request.param
    config.pluginmanager.register(DynamicFixturePlugin(), 'server-bin-fixture')

And I’m +1 to @argaen about some notes in CHANGELOG.