In contextlib, there is code which roughly looks like

        def _exit_wrapper(exc_type, exc, tb):
            return cm_exit(cm, exc_type, exc, tb)
        _exit_wrapper.__self__ = cm

This creates a new function _exit_wrapper from a given function cm_exit by prepending the __self__ attribute to *args. Now this is exactly what a method does too.

It would be better to use an actual method for this: it's cleaner, faster and it doesn't abuse a double-underscore attribute. The latter will actually break with PEP 575, as __self__ will become a special name  instead of an arbitrary attribute.