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In [44]: import networkx as nx
In [45]: import random
In [46]: G=nx.gnp_random_graph(10,0.5,directed=True)
In [47]: DAG = nx.DiGraph([(u,v,{'weight':random.randint(-10,10)}) for (u,v) in G.edges() if u<v])
In [48]: nx.is_directed_acyclic_graph(DAG)
Out[48]: True