text: #
  # Copyright 2016 Pixar
  #
  # Licensed under the Apache License, Version 2.0 (the "Apache License")
  # with the following modification; you may not use this file except in
  # compliance with the Apache License and the following modification to it:
  # Section 6. Trademarks. is deleted and replaced with:
  #
  # 6. Trademarks. This License does not grant permission to use the trade
  #    names, trademarks, service marks, or product names of the Licensor
  #    and its affiliates, except as required to comply with Section 4(c) of
  #    the License and to reproduce the content of the NOTICE file.
  #
  # You may obtain a copy of the Apache License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the Apache License with the above modification is
  # distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  # KIND, either express or implied. See the Apache License for the specific
  # language governing permissions and limitations under the Apache License.
  #
  #
  # A base class for all context menu items.
  # This provides a simple behavior to ensure that a chosen
  # context menu item is valid. This helps us avoid a situation
  # in which a user right-clicks in an area with no item but still
  # receives a context menu.
  #
  class UsdviewContextMenuItem():
      def isValid(self):
          ''' Menu items which have an invalid internal item are considered invalid.
              Header menus don't contain an internal _item attribute, so we
              return true in the case of the attribute being undefined.
              We use this function to give this state a clearer name.
          '''
          return not hasattr(self, "_item") or self._item is not None
  