How to use the envisage.api.contributes_to function in envisage

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        return self

    @contributes_to(PREFERENCES)
    def _get_preferences(self):
        filename = os.path.join(os.path.dirname(__file__), 'preferences.ini')
        return [ 'file://' + filename ]

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        return self

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        return self

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        """
        Gets the :mod:`envisage` plugin for this operation (usually `self`).

    @contributes_to(VIEW_PLUGIN_EXT)
    def get_plugin(self):
        return self

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        return self

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        return self

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        return self

    @contributes_to(OP_PLUGIN_EXT)
    def get_plugin(self):
        return self