'Return True if data differs from initial.'

def _has_changed(self, initial, data):

    if (data is None):
        data_value = u''
    else:
        data_value = data
    if (initial is None):
        initial_value = u''
    else:
        initial_value = initial
    if (force_unicode(initial_value) != force_unicode(data_value)):
        return True
    return False
