Huum, along with the new PyLint release, it's time to introduce the PyLint-Brain project I've recently started.
Despite its name, PyLint-Brain is actually a collection of extensions for ASTNG, with the goal of making ASTNG smarter (and this directly benefits PyLint) by describing stuff that is too dynamic to be understood automatically (such as functions in the hashlib module, defaultdict, etc.).
The PyLint-Brain collection of extensions is developped outside of ASTNG itself and hosted on a bitbucket project to ease community involvement and to allow distinct development cycles. Basically, ASTNG will include the PyLint-Brain extensions, but you may use earlier/custom versions by tweaking your PYTHONPATH.
Take a look at the code, it's fairly easy to contribute new descriptions, and help us make pylint smarter!