擅长:python、mysql、java
<p><a href="http://docs.python.org/2/library/types.html#types.NoneType">^{<cd1>}</a>只是<a href="http://docs.python.org/3/library/constants.html#None">^{<cd2>}</a>单例的类型:</p>
<pre><code>>>> type(None)
<type 'NoneType'>
</code></pre>
<p>从上面的后一个链接:</p>
<blockquote>
<p><strong><code>None</code></strong></p>
<p>The sole value of the type <code>NoneType</code>. <code>None</code> is frequently used to represent the absence of a value, as when default arguments are not passed to a function. Assignments to <code>None</code> are illegal and raise a <code>SyntaxError</code>. </p>
</blockquote>
<p>在您的例子中,您试图连接的项之一似乎是<code>None</code>,因此出现错误。</p>