Python: can call __subclasses__() on build in types, not on custom object
<pre><code>class Test: pass
print(Test.__subclasses__())
</code></pre>

<p>returns:</p>

<pre><code>AttributeError: class Test has no attribute '__subclasses__'
</code></pre>

<p>And</p>

<pre><code>print(int.__subclasses__())
</code></pre>

<p>returns:</p>

<pre><code>[&lt;type 'bool'&gt;]
</code></pre>

<p>Why can't I call <strong>subclasses</strong>() on my custom object?</p>

<p>This build in methods aren't reserver for custom types, are they?</p>

<blockquote>
  <p>Each class keeps a list of weak references to its immediate subclasses. This method returns a list of all those references still alive. Example:</p>
</blockquote>
