ycle is broken explicitly when the context manager
    exits.

    Storing the object (cm.unraisable.object) can resurrect it if it is set to
    an object which is being finalized. Exiting the context manager clears the
    stored object.

    Usage:

        with support.catch_unraisable_exception() as cm:
            # code creating an "unraisable exception"
            ...

            # check the unraisable exception: use cm.unraisable
            ...

        # cm.unraisable attribute no longer exists at this point
        # (to break a reference cycle)
    c