python，我如何将and if放入引发错误的函数

Question

嗨，我正在检查图中的循环

import networkx as nx
X2 = {"1": ["4"], "2": ["3"], "3": ["2", "4"], "4": ["1", "3"]}
L2 = []
for k,v in X2.items():
for i in range(len(v)):
L2.append((k,v[i]))
print(L2)
G = nx.DiGraph(L2)
G = G.to_undirected()
print(type(G))
print(nx.find_cycle(G))

在这种情况下，正确地没有循环，因此nx函数引发：

raise nx.exception.NetworkXNoCycle('No cycle found.')
networkx.exception.NetworkXNoCycle: No cycle found.

如果函数引发错误，我如何设置和If条件来打印某些内容？

Answer 1

使用；尝试"；以及"；除了"；关键字，读取python中的异常处理。

基本上你需要：

try:
your_function_call(arguments)
except nx.exception.NetworkXNoCycle as e:
print("Found the no cycle exception)

Answer 2

您在这里寻找的是错误处理。它的工作原理就像if，可以处理您想要的错误。

您可以通过try/except块来实现这一点。更多详细信息请点击此处。

import networkx as nx
X2 = {"1": ["4"], "2": ["3"], "3": ["2", "4"], "4": ["1", "3"]}
L2 = []
for k,v in X2.items():
for i in range(len(v)):
L2.append((k,v[i]))
print(L2)
try:
G = nx.DiGraph(L2)
G = G.to_undirected()
print(type(G))
print(nx.find_cycle(G))
except:
print("Error message")