def openBlob(blob, mode='r'):
    """ open a blob taking into consideration that it might need to be
        invalidated in order to be fetch again via zeo;  please see
        http://dev.plone.org/plone/changeset/32170/ for more info """
    try:
        return blob.open(mode)
    except IOError:
        blob._p_deactivate()
        return blob.open(mode)
