擅长:python、mysql、java
<p><code>None</code>是<a href="http://docs.python.org/2/library/constants.html" rel="nofollow noreferrer">constant</a>,是<code>types.NoneType</code>的唯一值(对于<a href="https://docs.python.org/2/library/constants.html?highlight=nonetype#None" rel="nofollow noreferrer">v2.7</a>,对于<a href="https://docs.python.org/3/library/constants.html?highlight=nonetype#None" rel="nofollow noreferrer">v3.x</a>)</p>
<p>无论如何,当您尝试从<code>types.NoneType</code>继承时</p>
<pre><code>from types import NoneType
class InvalidKeyNone(NoneType):
pass
foo = InvalidKeyNone()
print(type(foo))
</code></pre>
<p>你会得到这个错误</p>
<blockquote>
<p><em>Python 2</em></p>
<p>TypeError: Error when calling the metaclass bases
type 'NoneType' is not an acceptable base type</p>
<p><em>Python 3</em></p>
<p>ImportError: cannot import name 'NoneType'</p>
</blockquote>
<p>简而言之,您不能从<code>NoneType</code>继承</p>
<p>总之,为什么要让类继承<code>NoneType</code>?在</p>