实例如下：
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import numpy
from numpy import *
def dfs( v ):
vis[v] = -1
flag = 0
for i in range(n):
# print (a[v][i],'---', vis[i] )
if a[v][i] != 0 and vis[i] != -1:
dfs(i)
vis[i] = 1
else:
pass
if a[v][i] != 0 and vis[i] == -1:
print ('Yes, there is A loop in this network\n')
global swi
swi = True
exit()
return
# break
else:
pass
print ('s = 0')
return False
global swi
swi = False
'''===装载数据'''
edges = numpy.loadtxt('9_nodes_with_r_edge_8_to_3.txt')
# edges = [ int(i) for i in edges]
bian = int(shape(edges)[0]) - 1
print (bian,'edges in the network \n')
print (shape(edges),'\n')
n = int( edges[0][1] )
c = int( edges[0][0] )
# n, c = input().split()
# n = int(n)
# c = int(c)
a = [([0] * n) for i in range(n)]
vis = [0] * c
for i in range(1, c+1):
s, t = edges[i][0:2]
# print (s,' - ', t )
'''GO_OBO文件则 s, t 不需要 -1 '''
s = int(s) - 1
t = int(t) - 1
# s = int(s)
# t = int(t)
a[s][t] = 1
# print (a)
# print (vis)
dfs(0)
# print (swi)
if not swi:
print('No loop, DAG - DAG - DAG')
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用到 numpy 模块，读取的 txt 文件为 有向图的连边，其中第一行 第一个数字 为 边的数量，第二个数字为 节点数 第二行及以后 前两个数字，第一个为 起点， 第二个为 落点。
以上这篇Python 判断 有向图 是否有环的实例讲解就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：http://blog.csdn.net/sinat_35496345/article/details/70215842