title: What's the difference between declaring `class A` and `class A()`?
body: <p>We define class in python as following:</p>
  
  <pre><code>class A:
      def x(self):
          print("In x")
  </code></pre>
  
  <p>But i just made a typo and it executed successfully in linux cli with python version 3.7. Here it is:</p>
  
  <pre><code>class A():
      def x(self):
          print("In x")
  </code></pre>
  
  <p>What does this mean???</p>