code: def addEdgeToGraph(parentNodeName, childNodeName, graphFileHandle, colour="black", length="10", weight="1", dir="none", label="", style=""):
      
      graphFileHandle.write('edge[color=%s,len=%s,weight=%s,dir=%s,label="%s",style=%s];\n' % (colour, length, weight, dir, label, style))
      graphFileHandle.write("%s -- %s;\n" % (parentNodeName, childNodeName))
docs: Links two nodes in the graph together.