title: class A :, class A(object) :, or class A() :
body: <p>What is the exact difference among these three and when do we use what?</p>
  <pre><code>class A:
      pass
  </code></pre>
  <pre><code>class A(object):
      pass
  </code></pre>
  <p>or</p>
  <pre><code>class A():
      pass
  </code></pre>