def revert(namespace, name):

    """ revert to the orginal value the last patch modified.

        Raise ValueError if no such original value exists.

    """

    nref = (namespace, name)

    if nref not in patched or not patched[nref]:

        raise ValueError, "No original value stored for %s.%s" % nref

    current = getattr(namespace, name)

    orig = patched[nref].pop()

    setattr(namespace, name, orig)

    return current