pytest AttributeError: 'Function' object has no attribute 'get_marker'

Pytest has changed its API in version 4.

Quick solution: use get_closest_marker() instead of get_marker():

def pytest_collection_modifyitems(config, items):
    items.sort(key=lambda x: 2 if x.get_closest_marker('slow') else 1)

See https://github.com/pytest-dev/pytest/pull/4564

Remove Node.get_marker(name) the return value was not usable for more than a existence check.

Use Node.get_closest_marker(name) as a replacement.

Remove testfunction.markername attributes - use Node.iter_markers(name=None) to iterate them.