def _toFieldValue(self, input):
     value = super(Bytes, self)._toFieldValue(input)
     if type(value) is unicode:
         try:
             value = value.encode('ascii')
         except UnicodeError, v:
             raise ConversionError(_("Invalid textual data"), v)

 def addButtonLabel(self):
     button_label = _('Add %s')
     button_label = translate(button_label, context=self.request,
                              default=button_label)
     title = self.context.title or self.context.__name__
     title = translate(title, context=self.request, default=title)
     return button_label % title

 def _toFieldValue(self, input):
     if input:
         try:
             return self.convertTokensToValues([input])[0]
         except (InvalidValue, TypeError) as e:
             raise ConversionError(_("Invalid value"), e)
     else:
         return self.context.missing_value

 def _toFieldValue(self, input):
     if input == self._missing:
         return self.context.missing_value
     else:
         try:
             return int(input)
         except ValueError as v:
             raise ConversionError(_("Invalid integer data"), v)

 def _toFieldValue(self, input):
     """See SimpleInputWidget"""
     if input is None:
         input = []
     elif not isinstance(input, list):
         input = [input]
     try:
         values = self.convertTokensToValues(input)
     except InvalidValue, e:
         raise ConversionError(_("Invalid value"), e)

def BooleanRadioWidget(field, request, true=_('on'), false=_('off')):
    vocabulary = SimpleVocabulary.fromItems( ((true, True), (false, False)) ) 
    widget = RadioWidget(field, vocabulary, request)
    widget.required = False
    return widget

def BooleanSelectWidget(field, request, true=_('on'), false=_('off')):
    vocabulary = SimpleVocabulary.fromItems( ((true, True), (false, False)) )
    widget = SelectWidget(field, vocabulary, request)
    widget.size = 2
    widget.required = False
    return widget


def BooleanDropdownWidget(field, request, true=_('on'), false=_('off')):
    vocabulary = SimpleVocabulary.fromItems( ((true, True), (false, False)) )
    widget = DropdownWidget(field, vocabulary, request)
    widget.required = False
    return widget


_msg_true = _("True")
_msg_false = _("False")

class BooleanDisplayWidget(DisplayWidget):

    def __call__(self):
        if self._renderedValueSet():
            value = self._data
        else:
            value = self.context.default
        if value:
            return _msg_true
        else:
            return _msg_false