title: Why the super class is empty when define child class?
body: <p>When creating child class, specify the super class as empty.</p>
  
  <pre><code>class Foo1():pass
  class Foo2:pass
  </code></pre>
  
  <p>What is the different of Foo1 and Foo2.</p>
  
  <p>And there are some other class definition.</p>
  
  <pre><code>class Foo3(object):
  </code></pre>