... graph . ... 15 nodes -- set of elements . 16 lines -- {line: cost}. 17 line is frozenset([e1, e2]) . ... 41 def __init__ ( self , nodes = None , lines = None ): . ... 58 """ Return if these two nodes of the graph are bounded with line """ . ... 72 c = dict ([( node , 0 ) for node in self . ... 79 def drop_node ( self , node ): . ... 85 def add_node ( self , node , parent_graph ): . 86 """ Add node and corresponding lines from parent_graph . ... 97 def drop_nodes ( self , nodes ): . ...