code: def list_user_roles(self):
          
          _form = JsonForm(current=self.current, title=_(u"Switch Role"))
          _form.help_text = "Your current role: %s %s" % (self.current.role.unit.name,
                                                          self.current.role.abstract_role.name)
          switch_roles = self.get_user_switchable_roles()
          _form.role_options = fields.Integer(_(u"Please, choose the role you want to switch:")
                                              , choices=switch_roles, default=switch_roles[0][0],
                                              required=True)
          _form.switch = fields.Button(_(u"Switch"))
          self.form_out(_form)
docs: Lists user roles as selectable except user's current role.