'A network of nodes connected by edges that can be drawn with a given layout.'

def __init__(self, layout=SPRING, distance=10.0):

    self.nodes = []
    self.edges = []
    self.root = None
    self._adjacency = None
    self.layout = (((layout == SPRING) and GraphSpringLayout(self)) or GraphLayout(self))
    self.distance = distance
