擅长:python、mysql、java
<p>查看<a href="http://docs.python.org/tutorial/errors.html" rel="nofollow">Errors and Exceptions.</a>您可以这样做:</p>
<pre><code>def run(self,arg):
try:
return make_node(arg)
except AlreadyNodeError:
pass
</code></pre>
<p>在make_node函数中,如果参数已经是节点,则让它引发AlreadyNodeError。在</p>