'length: bar.STRETCH, bar.CALCULATED, or a specified length.'

def __init__(self, length, **config):

    command.CommandObject.__init__(self)
    self.name = self.__class__.__name__.lower()
    if ('name' in config):
        self.name = config['name']
    configurable.Configurable.__init__(self, **config)
    self.add_defaults(_Widget.defaults)
    if (length in (bar.CALCULATED, bar.STRETCH)):
        self.length_type = length
        self.length = 0
    else:
        assert isinstance(length, six.integer_types)
        self.length_type = bar.STATIC
        self.length = length
    self.configured = False
