why my code only print 'bbb' once,and it does not run wrong unexpectedly
<pre><code>class a:
    class __b__(object):
        print 'bbb'

b=a()
b.__b__()
b.__b__()
b.__b__()
a.__b__()
a.__b__()
a.__b__()
</code></pre>

<p>it print 'bbb' only once,
thanks</p>
