擅长:python、mysql、java
<p>你检查过你的<code>counter</code>字典至少有一个值符合<code>nb == n</code>条件吗?在我看来,结果要么是你的<code>sum</code>,要么是你的<code>len</code>返回<code>0</code>。。。</p>
<p>看看这个:</p>
<pre><code>>>> n = 3
>>> counter = {'a': 1}
>>> 100. / sum(1 for nb in counter.itervalues() if nb == n) / len(counter)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ZeroDivisionError: float division by zero
>>> counter = {'a': 3}
>>> 100. / sum(1 for nb in counter.itervalues() if nb == n) / len(counter)
100.0
</code></pre>