title: How to implement chain operations in Python?
body: <pre><code>class Array:
      def __init__(self):
          self.list = []
  
      def add(self, num):
          self.list.append(num)
  
  a = Array()
  a.add(1).add(2)
  </code></pre>
  
  <p>I would like to add number 1, 2 to self.list like this.
  How can I implement?</p>