class DxfDrawing(object):
    """
    Represents intermediate model of DXF drawing. It is useful in iterating
    through exported object and for easy change the DXF handling library.
    """
    def __init__(self):
        self._entities = {}
        self._layers = {}
        self._views = []
        self._vports = []
        self._blocks = []

    def isEmpty(self):
        return len(self._entities) == 0

    def addEntity(self, type, **kwargs):
        if type not in self._entities:
            self._entities[type] = []
        self._entities[type].append(kwargs)

    def addLayer(self, name, color):
        self._layers[name] = color

    def containsLayer(self, name):
        return name in self._layers

    def addBlock(self, block):
        self._blocks.append(block)

    def containsBlock(self, blockname):
        return blockname in self._blocks

    def convert(self, **kwargs):
        """ Converts this drawing into DXF representation object """
        raise NotImplementedError()