':return: a list of the canvas tags for all graphical
elements managed by this canvas widget, including
graphical elements managed by its child widgets.
:rtype: list of int'

def tags(self):

    if (self.__canvas is None):
        raise ValueError('Attempt    to    access    a    destroyed    canvas    widget')
    tags = []
    tags += self._tags()
    for child in self.__children:
        tags += child.tags()
    return tags
